WASHINGTON, March 31 - U.S. Secretary of State Antony Blinken on Wednesday called his Ukrainian counterpart Dmytro Kuleba to affirm Washington’s support for Ukraine’s territorial integrity amid growing signs that Russia may be preparing for an attack.

“The Secretary affirmed the United States’ unwavering support for Ukraine’s sovereignty and territorial integrity in the face of Russia’s ongoing aggression in the Donbas and Crimea,” Ned Price, a spokesperson at the Department of State, said in a statement.

The call comes amid growing concerns about Russia’s ongoing military buildup along the Ukrainian border that opens a possibility for a surprise attack within weeks.

The U.S. military’s European Command earlier this week has raised its watch level from ‘possible crisis’ to ‘potential imminent crisis’ responding to the deployment of the additional Russian troops.

The Kremlin said on Wednesday it was worried by the situation in eastern Ukraine, fearing the Ukrainian side could do something that would restart a civil war there, Reuters reported.

Russian President Vladimir Putin late on Tuesday accused Ukraine of provoking armed confrontation with pro-Russian separatists and failing to honor earlier agreements over its war-torn east, during a telephone call with France and Germany’s leaders.

In the call with Kuleba, Blinken “expressed concern about the security situation in eastern Ukraine and offered condolences on the recent loss of four Ukrainian soldiers,” Price said.

Ukraine’s armed forces said last week that four soldiers were killed in shelling by Russian forces in Donbass, the highest daily death total since a ceasefire agreement was reached last July.

Ukrainian Commander-in-Chief Ruslan Khomchak said on Tuesday Russia was building up armed forces near Ukraine’s borders in a threat to the country’s security.

Russia has recently delivered about 19,000 metric tons of fuel, 335 metric tons of ammunition, 35 heavy trucks, 3 tanks and multiple rocket launchers and special equipment to Donetsk and Luhansk regions, Khomchak said, citing Ukrainian intelligence reports.

This comes as NATO fighter jets scrambled 10 times on Monday to shadow Russian bombers and fighters during an unusual peak of flights over the North Atlantic, North Sea, Black Sea and Baltic Sea. In all, NATO aircraft intercepted six different groups of Russian military aircraft near Alliance airspace in less than six hours, according to a separate statement from NATO.

Russia explained the troop buildup by military exercises West-2021, which had concluded on March 23. The Russian troops were supposed to leave the area after the exercise, but they had failed to do so.

Moscow used similar tactic previously before attacking Ukraine in 2014 and Georgia in 2008. (tl/ez)