Washington/Kiev, April 3 : In their first-ever phone call, US President Joe Biden and his Ukrainian counterpart Volodymyr Zelensky discussed the escalating conflict in the Donbas region. During the call on Friday, Biden affirmed the US' "unwavering support for Ukraine's sovereignty and territorial integrity" and emphasised Washington's commitment to revitalise strategic partnership to support Zelensky's plan to tackle corruption and implement reforms, Xinhua news agency quoted the White House as saying in a statement. According to Zelensky's press service, the Ukrainian leader apprised Biden with the situation in Donbas, which has been heating up since the beginning of this year. Zelensky assured Biden of Ukraine's commitment to a peaceful settlement of the armed conflict in the region and pointed out the importance of maintaining a complete ceasefire for the continuation of negotiations between the Trilateral Contact Group and the Normandy Four. "We have the full and unwavering support of international partners, including Europe and the US. And one of the proofs of that is the conversation I had today with the President of the United States, Joe Biden. We discussed the situation in Donbas in detail. President Biden assured me that Ukraine would never be left alone against Russian aggression," Zelensky said. The two Presidents also discussed the implementation and continuation of reforms in Ukraine, including anti-corruption, judicial and Constitutional Court reform. Zelensky invited Biden to visit Ukraine and called on the US to take part in the Crimean Platform summit scheduled for August 23. The phone call followed at least three high-level calls between US and Ukrainian officials this week, which took place between Secretary of State Antony Blinken, Chairman of the Joint Chiefs of Staff Mark Milley, Pentagon chief Lloyd Austin and their Ukrainian counterparts. The New York Times reported that the US European Command in the past week raised its watch level from possible crisis to potential imminent crisis, the highest level, in response to the build-up of Russian forces on the border. The ongoing conflict in eastern Ukraine, which has claimed the lives of some 14,000 people and left as many as 40,000 wounded, began in April 2014. It further escalated on March 26 after four Ukrainian soldiers were killed. /IANS