WASHINGTON: President Joe Biden reaffirmed US support for Ukraine's territorial integrity Monday after Russian troop movements on its border, and invited President Volodymyr Zelensky to the White House.

National Security Advisor Jake Sullivan told reporters that Biden talked by phone with Zelensky, telling him "he will stand up firmly for Ukraine's sovereignty" and "looks forward to welcoming him to the White House this summer."

The invitation to visit in July marked a show of support for Ukraine ahead of Biden's summit with Russian President Vladimir Putin in Geneva next week.

White House press secretary Jen Psaki said the leaders had discussed the countries' "shared democratic values and Ukraine's Euro-Atlantic aspirations."

She said Biden "affirmed the United States' unwavering commitment to Ukraine's sovereignty and territorial integrity in the face of ongoing Russian aggression in Donbas and Crimea."

In a statement Zelensky accepted the invitation.

He said that in their phone call Biden had reaffirmed support for providing a pathway for Ukraine to join NATO, and Zelensky "also expressed gratitude" for a US plan to supply 900,000 Covid-19 vaccine doses to Ukraine.

The Biden administration has expressed strong support for Kiev as it faces Russia-allied separatists and 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.

The movement of heavy armor and an estimated 100,000 troops or more to Ukraine's border sent alerts through NATO over concerns that Russia might be preparing to invade Ukraine under the guise of conducting military exercises.