US President Joe Biden will welcome his Ukrainian counterpart Volodymyr Zelensky to the White House on August 30, press secretary Jen Psaki announced -- with Kiev likely to push for more support in its protracted war with Russian-backed separatists.

Washington has long backed Kiev in the dispute with Moscow, and Biden had initially launched his invitation to Zelensky in June.

But the date for the visit came shortly after the United States said it had reached an agreement with Germany on the controversial Nord Stream 2 pipeline that would threaten Russia with sanctions and seek to extend the transit of gas through Ukraine.

"The visit will affirm 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," Psaki said in a statement.

She also noted Washington's close cooperation with Kiev over energy security, and its backing for Zelensky's push to tackle corruption.

The Biden administration has expressed strong support for Kiev as it faces Russia-allied separatists in its east in a war which has left more than 13,000 people dead since 2014.

Ukraine also saw a strong buildup in April of Russian troops along its eastern border and in Crimea, the Ukraine territory seized seven years ago by Moscow.

Moscow said it was not threatening the country and has since pulled back some of the troops.

Ukraine remains concerned about the strength of US support.

It expressed concern over Biden's meeting with Russian leader Vladimir Putin in June, as well as Washington's decision at the time to drop sanctions aimed at blocking completion of the Nord Stream 2 pipeline.

Ukraine figured deeply in Biden's election fight against his predecessor Donald Trump.

Trump was impeached in 2019 after he pressured Zelensky, using aid as leverage, to hand over political dirt on Biden, who as vice president several years earlier had dealings with the country.

Without evidence, Republicans still maintain that Biden is protecting himself and his son Hunter over allegedly shady business deals done with Ukrainians.