Prime Minister Vladimir Putin accused the separatist region of Chechnya today of harboring and supporting terrorists who bombed three Russian apartment buildings in recent weeks, killing 276 people.

Russian soldiers, meanwhile, braced for a new conflict in the Caucasus region of southern Russia as Defense Minister Igor Sergeyev announced that Chechen guerrillas who have made incursions into the neighboring southern region of Dagestan since early August were massing on the border in preparation for a new offensive aimed at establishing an Islamic state there.

Meanwhile, in the aftermath of two deadly bombings of apartment buildings in Moscow, authorities intensified security checks of all 30,000 residential buildings in the city and said they had located a truck that may have brought explosives to to the city from southern Russia. They said the explosive material was concealed in sugar sacks and that between 1.5 and 1.8 tons that had been brought to Moscow--enough to blow up several buildings--was still missing. They also said a driver of a smaller truck used to distribute the explosives had confessed his role.

[Early Thursday, an apartment building in the southern city of Volgodonsk was heavily damaged by an explosion in which at least seven people were killed. Local residents told the Interfax news agency that a truck blew up next to the building, but that could not be immediately confirmed. Volgodonsk lies 300 miles north of Dagestan, where the Chechen rebels are fighting Russian troops.]

Following the latest blast in Moscow Monday, an unprecedented security sweep dubbed "Operation Whirlwind" was extended nationwide. Police said 27 people were detained, including three described as witnesses. "We have identified the people who carried out the explosion," said Moscow deputy police chief Alexander Veldyayev. "It is now an established fact the terrorist attacks were carried out by Chechen fighters. They used people with Slav appearances."

Putin said that "it is perfectly obvious for us now that terrorists hide on the territory of the Chechen republic and they are backed by extremist forces in Chechnya." He said the identity of the bombers had been discovered, but that they had not been located, and he demanded their extradition from Chechnya. Putin also reiterated a Russian claim that international terrorists were reinforcing the Chechen rebels.

The lower house of the Russian parliament, the State Duma, passed a resolution today criticizing "defects" in the 1996 cease-fire agreement between Russia and Chechnya. The truce, which came after two years of war that ended with Russian troops expelled from the region, called for a five-year waiting period before the determination of Chechnya's final status. Chechnya considers itself independent, but neither Russia nor any other country has recognized it as a sovereign state.

Chechen President Aslan Maskhadov's government has denied involvement in the bombings. Maskhadov has also denied that Chechnya is behind the cross-border attacks into neighboring Dagestan. But Russian analysts believe that Maskhadov has lost control of the guerrillas, who are under the command of prominent Chechen rebel commander Shamil Basayev.

The Tass news agency received an anonymous call today from a man who said the bombings were "acts of retribution for the terrorist actions of the Russian air force against civilians in Dagestan and Chechnya."