Amid a recent buildup of Russian troops along the Ukrainian border, United States Secretary of State Antony Blinken will visit Ukraine next month to show "unwavering" support for the country.

Russia in recent weeks deployed up to 100,000 troops near Ukraine's northern and eastern borders and in Crimea, raising concerns of a major escalation.

But last Friday, Moscow announced that it had started withdrawing its armed forces, with Kyiv and NATO welcoming the announcement.

Blinken's May 5-6 visit is intended "to reaffirm unwavering U.S. support for Ukraine's sovereignty and territorial integrity in the face of Russia's ongoing aggression," said a statement from Blinken's spokesperson Ned Price.

Blinken is to meet Ukraine's President Volodymyr Zelenskiy during the stopover.

Kyiv has been battling pro-Russian separatists in the eastern Donetsk and Lugansk regions since 2014, following Moscow's annexation of the Crimean peninsula.

A cease-fire that took hold last July has been shredded this year, with clashes sharply increasing between Ukrainian forces and separatists since January.

The separatists are widely seen as having Russia's political and military backing – which Moscow denies – in the conflict that has claimed more than 13,000 lives.