NATO Secretary General Anders Fogh Rasmussen on Tuesday said he could not confirm the withdrawal of Russian troops from near the Ukrainian border as announced by the Kremlin.

"Unfortunately I cannot confirm that Russia is withdrawing its troops; this is not what we have seen," Rasmussen told journalists ahead of a NATO foreign ministers meeting on the crisis in Ukraine.

Ukraine and the United States have accused Russia of massing thousands of troops near the border and have expressed concern that Moscow intends to seize southeastern parts of Ukraine that are home to large populations of ethnic Russians, following the Crimea takeover.

German Chancellor Angela Merkel's office said Putin had personally informed her of the troop pullback in a telephone conversation on Monday, and Foreign Minister Frank-Walter Steinmeier called the move "a small sign that the situation is becoming less tense".

Ukraine also reported Monday that Russian troops were leaving the flashpoint area.

NATO foreign ministers are meeting at the alliance headquarters in Brussels to forge a response to Russia's annexation of Crimea last month.

But as the talks began, NATO seemed to be stepping back from reinforcing military presence in countries bordering Russia, preferring for now to give more time to diplomacy.

"I think everybody realises that the best way forward is a political and diplomatic dialogue," Rasmussen said, though he added NATO was "very determined to provide effective defence and protection of our allies".

One counter-measure apparently off the table for now is the idea to set up permanent military bases in NATO countries bordering with Russia.

The move would be highly controversial for Moscow, reversing an informal agreement made when NATO expanded east to include former Warsaw Pact countries that were eager to break away from years of Soviet domination.

But Dutch foreign minister Frank Timmermans said that for now "we don't need NATO troops at the border with Russia," adding there was "no need for sudden moves".

The cautious line could come as a disappointment to eastern NATO members, who were expected to argue for a tougher stance against Russia at the meeting.

"There is a rather wide consensus among the allies, even if eastern countries -- such as the Baltics and Poland -- wish NATO would adopt a more pronounced stand against Russia," a diplomat said.

Before entering NATO headquarters for the talks, Polish Foreign Minister Radoslaw Sikorski said his country "would welcome any forces" on its territory.

"All members should enjoy the same level of security," he said.