WASHINGTON—The U.S. is closing its embassy in the Ukrainian capital of Kyiv and relocating operations 340 miles west to Lviv near the Polish border, as allies warn that an attack by Russian forces on Ukraine may be imminent.

Secretary of State Antony Blinken described the relocation as a temporary move to protect embassy staff.

“These prudent...

WASHINGTON—The U.S. is closing its embassy in the Ukrainian capital of Kyiv and relocating operations 340 miles west to Lviv near the Polish border, as allies warn that an attack by Russian forces on Ukraine may be imminent.

Secretary of State Antony Blinken described the relocation as a temporary move to protect embassy staff.

“These prudent precautions in no way undermine our support for or our commitment to Ukraine,” Mr. Blinken said Monday. “Our commitment to Ukraine’s sovereignty and territorial integrity is unwavering.”

As part of the move, the State Department ordered the destruction of networking equipment and computer workstations and the dismantling of the embassy telephone system, according to U.S. officials familiar with the matter and internal communications reviewed by The Wall Street Journal. Those moves render the Kyiv embassy inoperable as a diplomatic facility.

On Sunday, 56 embassy workers and the embassy’s classified materials arrived at Dulles International Airport near Washington, the internal communications said.

Ukrainian law enforcement conducted drills that included mock protests and riots Saturday in Kalanchak, a town some 20 miles north of the Crimean peninsula. The training simulated hybrid-warfare tactics used by Russia in 2014. Photo: Oleg Petrasyuk/Shutterstock The Wall Street Journal Interactive Edition

The State Department said it had taken all necessary precautions to protect classified materials as part of the drawdown.

A day earlier, the U.S. Embassy in Kyiv said most of its diplomats had been ordered to leave Ukraine amid the acute threat of a Russian attack, with only a core group of diplomats staying behind in Lviv. A senior U.S. official had maintained, however, that the embassy would remain open in Kyiv and the State Department wasn’t suspending operations of the embassy.

Mr. Blinken on Monday spoke with his Ukrainian counterpart, Dmytro Kuleba, and assured him that the U.S. remained committed to Ukraine’s long-term economic stability and security.

State Department spokesman Ned Price told reporters Monday that the U.S. is grateful to the National Guard of Ukraine, which will be guarding the embassy facility in Kyiv, and added, “It is certainly our intention to return to that embassy in Kyiv just as soon as it is safe for us.”

The relocation to Lviv allows the U.S. to maintain a diplomatic presence on the ground in Ukraine while positioning the remaining U.S. diplomats closer to the Polish border in the event of a Russian attack. Kyiv’s location, not far from border areas where Russian troops are stationed, means the Ukrainian capital is at higher risk of violence if Russia decides to invade, Mr. Price said.

Ukrainian officials have argued that the U.S. and other Western countries have overstated the prospect of a potential Russian invasion and have said that Moscow’s effort to destabilize Ukraine is the main danger. They have warned that the removal of diplomats from Kyiv is giving the impression that the capital is about to fall.

Mr. Price said, “It remains unclear to us whether Russia is interested in pursuing a diplomatic path” regarding Ukraine.

“It is a distinct possibility, perhaps more real than ever before, that Russia may decide to proceed with military action,” Mr. Price said.

Write to Vivian Salama at vivian.salama@wsj.com and Alan Cullison at alan.cullison@wsj.com