Strong domestic political support for Russia's offensive in Chechnya cracked for the first time today when Grigory Yavlinsky, leader of the Yabloko faction in parliament, called for peace talks and a halt to the bombing.

His demand came as Prime Minister Vladimir Putin rejected suggestions from the United States that the bombing campaign violated international conventions on warfare. Meanwhile, a Russian government spokesman immediately rejected Yavlinsky's appeal for peace talks.

After a cabinet meeting today, Moscow decided to impose a blockade on transport to and from the separatist region, closing off airports, roads and docks that link Russia and overseas points with Chechnya.

Yavlinsky, who earlier had backed a strong military action, said the Russian troops had gone far enough and created conditions for talks with Chechen President Aslan Maskhadov. His appeal marked the first time that a major political figure has called for a halt in military operations. His remarks may aggravate Russian commanders, who have warned against any order to pull back the troops or conduct any negotiations with the Chechens.

The military said it originally had planned only to seal off Chechnya at the border, but in recent weeks troops have taken more than a third of Chechen territory and are bombarding the capital of Grozny from its outskirts.

Yavlinsky said he was worried about the tide of refugees fleeing Chechnya, the "threat of a broad-scale winter guerrilla war," the growing evidence of civilian victims and reports in Moscow of friction between the military and political leadership. He said Russia's strategy in Chechnya is "unclear" and "all this leads to a serious political destabilization."

"The Russian armed forces have fulfilled their mission," Yavlinsky said, adding that they have "created for the first time over the last five years convincing preconditions for conducting a political process."

Yavlinsky demanded that Russia "stop the massive bombing of the territory of the Chechen republic" and "suspend broad-scale ground offensive operations." He also suggested taking up Maskhadov's offer of talks.

But Yavlinsky said he would insist that Chechnya release hostages, halt kidnappings and slave trade, extradite to Russia or elsewhere those responsible for a series of terrorist attacks in Russia and take "decisive" measures to disarm Chechen guerrillas. He added that if after 30 days Chechnya refused to talk, he would allow civilians to leave Chechnya and the Russian forces would be free to open fire again.