President Joe Biden reaffirmed US support for Ukraine's territorial integrity on Monday 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 marked a show of support for Ukraine ahead of Biden's summit with Russian President Vladimir Putin in Geneva next week.
In a statement, Zelensky accepted the invitation to visit in July.
He said that in their phone call Biden reaffirmed "unwavering support" for Ukraine and for providing a pathway for Ukraine to join Nato.
Zelensky "also expressed gratitude for the decision of the United States to provide Ukraine with 900,000 doses of vaccine against the COVID-19," the statement said.
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 armour 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.
Moscow said it was not threatening the country and has since pulled back some of the troops.
In March the Biden administration signalled its support by approving $125 million in military aid to Ukraine, with another $150 million on hold until Kiev can demonstrate progress on military reforms.
Ukraine though remains concerned about the strength of US support.
It has expressed concern over the timing of the Biden-Putin meeting, as well as Washington's decision to drop sanctions aimed at blocking the completion of the Nord Stream 2 pipeline set to deliver natural gas from Russia to Germany, bypassing Ukraine.
"Nord Stream 2 is not an economic project. It poses a serious threat and is a security challenge," the Zelensky statement said.
Biden meanwhile faces the likelihood of stepped-up political attacks from the right over meeting Zelensky, after Ukraine figured deeply in his election fight last year against former president Donald Trump.
Trump was impeached 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 Biden over allegedly shady business deals done with Ukrainians.
While Biden was vice president, Hunter Biden was on the board of one of the country's largest energy firms, with the company apparently having hoped to exploit him for his political connections.