The Russian-led breakaway regions of eastern Ukraine mobilized able-bodied men against what they said was an imminent attack by Kyiv, as shelling across the front line intensified, killing two Ukrainian soldiers.

Kyiv dismissed the call-up and moves to evacuate civilian residents of Russian-held Donetsk and Luhansk areas to Russia as a provocation. The escalation followed Western warnings that Moscow is about to launch an all-out invasion of Ukraine.

“It’s...

The Russian-led breakaway regions of eastern Ukraine mobilized able-bodied men against what they said was an imminent attack by Kyiv, as shelling across the front line intensified, killing two Ukrainian soldiers.

Kyiv dismissed the call-up and moves to evacuate civilian residents of Russian-held Donetsk and Luhansk areas to Russia as a provocation. The escalation followed Western warnings that Moscow is about to launch an all-out invasion of Ukraine.

“It’s a fake mobilization in response to a fake threat,” said Ukrainian Interior Minister Denys Monastyrskiy, who came under shelling near the front line on Saturday. “What they are trying to do is to create panic and fear, also on our side and among our people.”

Russian-installed authorities in Donetsk and Luhansk on Friday night instructed the areas’ women, children and elderly to leave for Russia, organizing convoys of buses. On Saturday, Denis Pushilin, head of the self-proclaimed Donetsk People’s Republic, ordered the general mobilization of men between 18 and 55 years old, including reservists, telling them to report to enlistment offices. Men of that age were banned from leaving the enclave.

“I appeal to all the men of the Republic, who are able to hold weapons in their hands, to stand up for their families, their children, wives, mothers,” Mr. Pushilin said in a televised address. Russian-installed authorities in Luhansk announced a similar decision.

Ukraine denies it has any plans to recapture by force the parts of Donetsk and Luhansk that Russian-backed forces seized in 2014. President Biden has said that he expected his Russian counterpart, Vladimir Putin, to invade Ukraine in the coming days, with targets including the Ukrainian capital.

Residents of the self-proclaimed Donetsk People’s Republic were being evacuated to Rostov region, Russia, on Saturday.

Photo: arkady budnitsky/Shutterstock/EPA

Some two million people live in the Russian-controlled parts of Donetsk and Luhansk, and Russian authorities said they are bracing for hundreds of thousands of refugees. Moscow promised each of these refugees accommodation and a $130 cash bonus.

Kyiv has said that while the security situation is deteriorating, it doesn’t share Washington’s apocalyptic predictions. Speaking Saturday at the Munich Security Conference, where he received a standing ovation, President Volodymyr Zelensky said Ukraine isn’t living in a delusion but continues to carry on in the face of an existential threat.

“Just putting ourselves in coffins and waiting for foreign soldiers to come in is not something we are going to do,” he said. “But we stand ready to respond to everything.”

Until last week shelling and firing incidents along the front line averaged five to six a day, but that number has surged more than 10-fold in the last three days, said Lt. Gen. Oleksandr Pavliuk, the commander of Ukrainian forces in Donbas.

“The enemy artillery is shooting from behind civilians,” he said. “And, in accordance with our principles, we do not fire back at civilians.”

Washington and Kyiv have warned that Moscow is looking to use fighting in Donetsk and Luhansk, where roughly 14,000 people have died since Russia fomented an uprising in 2014, as a pretext for a broader military operation against Ukraine. Russian officials said Saturday that two artillery shells fell inside Russia near the border, causing no damage. Kyiv denied its forces fired in that direction.

Mr. Monastyrskiy, citing Ukrainian intelligence, said Russian mercenaries from the Wagner group have arrived in Donetsk and Luhansk with orders to blow up critical infrastructure and pin the blame on Kyiv. The claim couldn’t be independently confirmed.

Shelling could be heard throughout Saturday in Stanytsia Luhanska, the Ukrainian-controlled town where the only crossing point between Russian-held areas and Ukrainian parts of Donbas—as the Donetsk and Luhansk regions are collectively known—operates daily.

Images released by Russia’s Defense Ministry on Saturday showed Russia test-launched ballistic and cruise missiles in what it described as strategic deterrence exercises. President Vladimir Putin oversaw the launches from a command center, according to a Kremlin pool report. Photo: Russian Defense Ministry/AFP via Getty Images The Wall Street Journal Interactive Edition

So far, the crossing has remained open, with more than 840 people, mostly women and children, traversing the front line to enter Ukrainian-controlled areas on Saturday, according to Ukrainian border officials. Some 50 fighting-age men were prevented by Russian-installed officials from leaving, they said.

“Of course, some of the people who cross this way are nervous and afraid, but we don’t see any panic so far,” said the Ukrainian governor of Luhansk region, Serhii Haidai, who was visiting the town. He said Russian authorities have started amassing heavy weapons on the other side of the front line.

Ukrainian authorities were preparing plans for evacuating civilians from towns within Russian artillery range, like Stanytsia Luhanska, should violence continue to escalate. Schools in those areas will operate remotely after shelling hit a kindergarten in Stanytsia Luhanska and an elementary school in a nearby town on Thursday, Mr. Haidai said. Ukraine and the U.S. blamed Russia for the shelling, which injured three staff members. None of the 20 kindergarten children in the building at the time were hurt when an artillery round punched through the brick wall of a recreation room.

Speaking next to a crater caused by one of the shells in the courtyard of the Stanytsia Luhanska kindergarten, Iryna Vereshchuk, Ukraine’s deputy prime minister and minister for the reintegration of occupied territories, said Moscow sought to create panic in Russian-held parts of Donetsk and Luhansk by spreading false plans of an alleged Ukrainian offensive and staging explosions there.

“What they need is fear,” she said.

Russian President Vladimir Putin and his Belarusian counterpart, Alexander Lukashenko, oversaw the test launch of ballistic missiles on Saturday.

Photo: alexey nikolsky/Agence France-Presse/Getty Images

Ms. Vereshchuk added that Kyiv doesn’t expect Russia to openly invade Ukraine imminently. “Our intelligence doesn’t confirm this. Yes, there are steps toward a certain escalation—you can hear shelling with your own ears—but that doesn’t mean that a full-scale invasion is being prepared. What our intelligence does confirm is that Russia is seeking to create provocations.”

Ukraine, she said, had no intention of retaking Russian-controlled areas by force. “We cannot start shooting peaceful residents,” she said.

Col. Oleksii Vukolov, deputy commander of the Ukrainian military’s Northern Command in Donbas, said the situation along the front line was tense but stable on Saturday.

“We observe the agreements and do not respond to fire. They are trying to provoke us to shoot back, so that they could say that the temporarily occupied areas are being assaulted,” Col. Vukolov said. “Our children are behind our backs, and we must defend them so they can live on this land in peace.”

According to U.S. estimates, as many as 190,000 Russian troops have deployed around Ukraine, ready to strike. Speaking at the conference in Munich, Vice President Kamala Harris—who met with Mr. Zelensky there—said Russia was following a playbook of aggression that the West has seen before, in which it will “create false pretext for invasion and it will amass troops and firepower in plain sight.”

Ukrainian soldiers near a military base close to Donetsk, Ukraine.

Photo: MANU BRABO FOR THE WALL STREET JOURNAL

Civilians took part in a military training course in Kyiv, Ukraine, on Saturday.

Photo: Chris McGrath/Getty Images

In an emotional speech, Mr. Zelensky pointed out that Ukraine gave up its nuclear weapons after the fall of the Soviet Union in return for security assurances from the U.S., U.K. and Russia. “Now, we have neither weapons, nor security, and we lost a part of our territory that is larger that Switzerland, Netherlands or Belgium.”

Mr. Zelensky questioned U.S. intelligence reports that a Russian invasion was imminent, but said Ukrainians would defend themselves with or without Western support. “We cannot remain passive,” he said. “We cannot say on the daily basis that war will happen tomorrow…How can you live in this state, when on a daily basis you are being told that tomorrow, the war will happen; tomorrow the advance will happen?”

Vice President Kamala Harris said the U.S. and its allies would impose sweeping economic sanctions and export controls against Russia to target financial institutions, key industries and “those who aid and abet” an unprovoked invasion of Ukraine. Photo: Tobias Hase/Associated Press The Wall Street Journal Interactive Edition

Russian military exercises that involve some 30,000 troops in Belarus are slated to end on Sunday. Russia has repeatedly said it intends to pull back these troops. Military experts say this deadline puts pressure on Mr. Putin, who must decide whether to send troops back to their bases or use them in an offensive operation against Ukraine.

The Ukrainian army has deployed and is on high alert, but until now hasn’t mobilized civilians, as pro-Kremlin authorities in Donbas have done. Ukrainian officials say that the shelling, which has increased all along the front lines as tensions with Moscow have worsened, is mostly exploratory, with Russian-backed forces seeking to provoke counterstrikes by Ukrainian units.

Residents from separatist-controlled regions in eastern Ukraine arrived at a tent camp in Russia’s Rostov region on Saturday.

Photo: SERGEY PIVOVAROV/REUTERS

On Saturday, Ukrainian defense officials said Russian-led fighters in Donbas distributed phony leaflets, allegedly from the Ukrainian military, to residents warning that Ukrainian forces would soon launch an attack on their territory.

In the Ukrainian-controlled city of Kramatorsk, less than an hour’s drive from the front line, many residents say they intend to stay whatever happens. Valentyna Skrybalo, 62, marched with a blue-and-yellow Ukrainian flag in central Kramatorsk in a rally commemorating the eighth anniversary of the street fighting in Kyiv that ousted a pro-Russian president in 2014.

“Putin has put his tanks and armor and soldiers on our border,” she said. “I have no plans to leave, this is exactly where I should be.”

Anastasia Shlepchenko, 32, said she was in Kyiv studying in 2014 but has since returned to be closer to her family. If a military invasion begins, she said she plans to stay no matter what happens. She said she respects Russians but pities their inability to choose their own political future under Mr. Putin’s rule.

“Ukraine is deciding its own future. That’s what all this is about, Ukraine deciding how it wants to live,” she said.

Ukrainian soldiers on the front line in Donetsk region, Ukraine, on Saturday.

Photo: GLEB GARANICH/REUTERS

—Ann M. Simmons in Moscow and Laurence Norman in Berlin contributed to this article.

Write to Yaroslav Trofimov at yaroslav.trofimov@wsj.com, Alan Cullison at alan.cullison@wsj.com and Thomas Grove at thomas.grove@wsj.com