U.S. defense officials reassure Ukraine of support amid tension with Russia

April 1 (UPI) -- Defense Secretary Lloyd Austin spoke to Ukraine's minister of defense on the phone Thursday to express "unwavering U.S. support for Ukraine's sovereignty" and to condemn Russian aggression in the country.

According to a readout from the Pentagon, Austin spoke with his Ukrainian counterpart, Andrii Taran, to discuss the regional security situation and expressed his condolences on the deaths of four Ukrainian soldiers last week.

Ukrainian officials say the soldiers were killed by Russian forces in Donbass, which the United States considers a violation of a ceasefire agreement.

"Russia's destabilizing actions undermine the de-escalation intentions that had been achieved through [last year's agreement]," Pentagon spokesman John Kirby said Wednesday, according to CNN. "Additionally, we are aware of Ukrainian military reports concerning Russian troop movements on Ukraine's borders."

Austin's call follows a Wednesday call between Secretary of State Antony Blinken and Ukrainian Foreign Minister Dmytro Kuleba to discuss recent security concerns, including last week's deaths.

Chairman of the Joint Chiefs of Staff Gen. Mark Milley also spoke with his Ukrainian counterpart, Ruslan Khomchak, according to a readout released by the military, and with Russian Gen. Valery Gerasimov.

Milley's call with Komchak concerned "the current security environment in Eastern Europe," but the readout of the call with Gerasimov said both parties have agreed to keep the details of the conversation private "in accordance with past practice."

In his conversation with Taran, Austin also reportedly reiterated that the United States is committed to building the capacity of Ukraine's forces to "defend more effectively against Russian aggression," the Pentagon said.

The United States has committed more than $2 billion in security assistance to Ukraine since 2014, the Pentagon noted.

That figure includes a $125 million package announced last month to fund armored patrol boats, radar units and military medical equipment.

Russia annexed Crimea in 2014, and subsequent skirmishes between Ukrainian troops and pro-Russian separatists in the eastern part of the country have killed an estimated 14,000 people.

Tensions between the United States and Russia have also increased under President Joe Biden's administration

In March, Biden said Russian President Vladimir Putin would "pay a price" for interfering in the 2020 election, and called him "a killer."

Earlier this week NATO announced that alliance aircraft scrambled 10 times and intercepted six groups of Russian aircraft flying near alliance airspace.