KYIV, April 1 – U.S. Secretary of Defense Lloyd Austin called Defense Minister Andriy Taran on Thursday to assure Ukraine of an ‘unwavering support’ amid escalating tensions with Russia, the Department of Defense said in a statement.

The call comes a day after U.S. Secretary of State Antony Blinken called his Ukrainian counterpart Dmytro Kuleba amid signs of Russian military buildup near the Ukrainian border, signaling a potential attack.

“Secretary Austin reaffirmed unwavering U.S. support for Ukraine’s sovereignty, territorial integrity, and Euro-Atlantic aspirations,” the statement said. Austin “reiterated the U.S. commitment to building the capacity of Ukraine’s forces to defend more effectively against Russian aggression.”

Separately, Defense Attaches from the U.S., Canada and the U.K. had a meeting with Taran and top Ukrainian army commanders to discuss the situation and ways of reacting to the potential escalation.

“We stand with Ukraine as it defends its sovereignty and territorial integrity and are watching the situation in Ukraine closely,” the U.S. Embassy said in a statement posted on Twitter.

The flurry of phone calls between senior U.S. and Ukrainian officials over the past three days shows the level of concern over increasingly provocative movements of Russian troops along the Ukrainian border.

"The strategic dialogue at the level of defense ministers is not just taking place, but is developing dynamically,” Taran said in a statement after the call with Austin. “The American partners are actively initiating contacts, expressing sincere concern about Russia's attempts to aggravate the situation around Ukraine.”

Russia has accumulated a significant number of troops near the borders with Ukraine and within the occupied regions of Crimea and parts of Donetsk and Luhansk to the level the poses a security threat, according to Ukrainian military command.

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 Russian troops in the area.

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, according to Ukrainian Commander-in-Chief Ruslan Khomchak.

Since 2014, the U.S. has committed more than $2 billion in security assistance to Ukraine, including a recently announced $125 million package that featured defensive weapons and other key capabilities to enhance the lethality, command and control, and situational awareness of Ukraine’s Armed Forces.

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. (tl/ez)