US national security adviser John Bolton arrived in Kiev on Tuesday for talks with President Volodymyr Zelensky, a day after the announcement of a new peace summit on eastern Ukraine.
"Ambassador Bolton is here to underscore US support for Ukraine's sovereignty, territorial integrity and Euro-Atlantic path," the US Embassy said on social media.
Bolton will hold talks with Zelensky and other Ukrainian officials.
"I'm looking forward to my upcoming meetings with our partners in Kyiv," Bolton wrote on Twitter ahead of the trip.
"We support President Zelensky's reform efforts and vision to create a stronger and more prosperous Ukraine," he added.
French President Emmanuel Macron announced Monday that the leaders of Russia, Ukraine, Germany and France would hold peace talks on the conflict in September, but did not give an exact date.
Ukraine has been locked in conflict with Russia-backed separatists since Moscow annexed Crimea in 2014, a move the international community refuses to recognise.
Some 13,000 people have been killed in the violence that Kiev blames on Russian President Vladimir Putin.
Moscow has denied claims it has funnelled troops and arms across the border.
The last Ukraine peace summit between the four countries was held in 2015.