MOSCOW, May 7 - Russian President Vladimir Putin called on pro-Moscow separatists in Ukraine to postpone a vote on secession just five days before it was to be held, potentially pulling Ukraine back from the brink of violent dismemberment, Reuters reported.

It was the first sign the Kremlin leader has given that he would not endorse a referendum planned for Sunday by pro-Russian rebels seeking independence for two provinces in the east, and Russian analysts said they believed the rebels would heed Putin's call to put off the vote.

In what could be a breakthrough in the worst crisis between East and West since the Cold War, Putin also announced he was pulling Russian troops back from the Ukrainian border.

NATO, the Pentagon and the White House all said they had seen no signs of a Russian pull-back from the frontier, where Moscow has massed tens of thousands of troops, proclaiming the right to invade Ukraine to protect Russian speakers.

But Putin's comment suggested that any Russian military incursion into eastern Ukraine was off the agenda for now.

"We call on the representatives of southeastern Ukraine, the supporters of the federalization of the country, to postpone the referendum planned for May 11," Putin said.

He said this would create conditions for dialogue between the Ukrainian authorities in Kiev and the separatists.

"We're always being told that our forces on the Ukrainian border are a concern. We have withdrawn them. Today they are not on the Ukrainian border, they are in places where they conduct their regular tasks on training grounds," Putin said.

Putin spoke in Moscow after talks with the head of the Organization for Security and Cooperation in Europe, who said the security and rights body would soon propose a "road map" to defuse the Ukraine crisis.

A pro-Russian separatist leader said the separatists would consider Putin's call to postpone their referendum at a meeting of their self-proclaimed People's Assembly on Thursday.

"We have the utmost respect for President Putin. If he considers that necessary, we will of course discuss it," Denis Pushilin told Reuters in Donetsk, a city of 1 million people which the rebels have proclaimed capital of an independent "People's Republic of Donetsk.”

Ukrainian Prime Minister Arseniy Yatseniuk dismissed as "hot air" Putin's call for the referendum to be postponed.

The White House said the "illegitimate, illegal" vote should be cancelled rather than postponed.

Ukrainian government troops have launched a military campaign to retake territory held by separatists this week. Troops briefly captured the rebel-held city hall in the eastern port of Mariupol overnight, but quickly abandoned it, leaving it back in the hands of the separatists.

Witnesses said the soldiers left after smashing furniture and office equipment. The smell of tear gas hung in the air inside the building which was largely empty in the morning, with activists in gas masks clearing debris.

Pro-Russian activists were rebuilding barricades outside the building where separatist flags flew and patriotic songs blared from loudspeakers.

In a boost for the rebels, one of their leaders, Pavel Gubarev, was released from detention in exchange for three members of the Ukrainian security services, a spokesman for the separatists' military headquarters in Slavyansk said. (rt/ez)