MOSCOW - Top US and Russian officials met Friday in Russia's westernmost outpost to discuss the Ukraine crisis amid attempts to bolster a fragile truce in the east of the ex-Soviet country, a source told AFP.

US Assistant Secretary of State Victoria Nuland and top Kremlin aide VladislavSurkov met near the city of Kaliningrad in Russia's exclave bordering European Union members Lithuania and Poland, a source familiar with the situation told AFP.

"The meeting is closed to the media. The topic is Ukraine," the source said.

The meeting took place in Russia because Surkov has been targeted by Western sanctions over the Kremlin's role in the Ukraine crisis and is unable to travel to the EU, the source said.

It came after Russian President Vladimir Putin and US President Barack Obama discussed the Ukraine crisis by phone earlier this week.

The White House said the Russians needed to "live up to the commitments that they made in Minsk -- to end their support for separatists that are destabilising Ukraine right now."

Putin for his part laid the blame for the simmering violence on Kiev, saying the Ukrainian authorities must establish "direct dialogue" with separatists in the east and agree constitutional amendments with them, among other requirements.

Ukrainian President Petro Poroshenko on Thursday said he wanted EU and US help in securing the return of Crimea, annexed by Russia in 2014, and vowed to win back the separatist east this year. (AFP)