President Vladimir Putin said Friday the Kremlin was preparing to take preventive action against terrorists, even as a Chechen rebel leader purportedly claimed responsibility for a series of attacks that killed hundreds of people and threatened more violence.

Putin's comments were the highest-level warning yet that Russia could take pre-emptive action against terror groups after the Sept. 1-3 deadly school hostage-taking in Beslan (search).

Lower-level officials have threatened anti-terror strikes abroad, and it was not immediately clear whether Putin was referring to actions only at home or outside Russia's borders.

"Now in Russia, we are seriously preparing to act preventively against terrorists," Putin said, according to the Interfax news agency. It quoted him as saying that the steps would be "in strict accordance with the law and norms of the constitution, relying on international law."

Recalling the attempts to appease Adolf Hitler in the 1930s, Putin said there could be no "bargaining" with terrorists.

"Every concession leads to a widening of their demands and multiples the losses," Putin was quoted as saying.

"In this war there is no rear or neutral zone, and where terrorists don't meet the necessary resistance, their bases and coordination centers crop up," Putin said.

His speech came the same day that an e-mail attributed to radical Chechen rebel leader Shamil Basayev (search) was posted on a Web site, claiming responsibility for an August explosion at a bus stop outside Moscow, the near-simultaneous bombings of two planes the same night, a suicide bombing outside a Moscow subway station a week later, and the Beslan hostage-taking, which ended in gunfire and explosions.

More than 430 people were killed in the attacks, with some 338 of those deaths coming during the Beslan siege.

The e-mail attributed to Basayev and posted Friday on the Kavkaz-Center (search) Web site said he had written to Putin proposing "independence [for Chechnya] in exchange for security."

It was impossible to confirm the authenticity of the message, which was signed with Basayev's nom de guerre, "Abdallakh Shamil, Emir of the Riyadus Salikhin Martyrs' Brigade." But the Web site is considered a mouthpiece for Basayev, and his previous claims of responsibility have appeared there.

The letter to Putin said if Moscow withdrew its troops and recognized Chechen independence, Chechnya (search) would neither support nor finance groups fighting the Kremlin, and "we can guarantee that all of Russia's Muslims would refrain from armed methods of struggle against the Russian Federation, at least for 10-15 years, on condition that freedom of religion (as is guaranteed in the Russian Federation) be respected."

But Basayev also threatened more attacks, saying Russia had forced his hand.

"They are fighting us without any rules, with the direct connivance of the whole world, and we are not bound by any circumstances or by anybody, and will fight by our rules," he wrote.

He also put the ultimate blame for the siege on Putin, accusing Russian forces of storming the school and causing the deaths.

"A terrible tragedy occurred in the city of Beslan; the Kremlin vampire destroyed and wounded 1,000 children and adults, giving the ordering to storm the school for the sake of imperial ambitions and the preservation of his own throne," the e-mail said.

Putin and other officials said repeatedly that they had not planned to storm the school, where the attackers had rigged bombs amid the approximately 1,200 hostages.

According to Russian officials and witnesses, explosions rocked the school as authorities tried to collect bodies, and armed volunteers began shooting, then the special forces opened fire, too.

The e-mail disputed that, saying Russian special services planned to storm the school "from the very beginning." It alleged that Emergency Situations Ministry workers who entered the school to purportedly collect bodies were really security service officers, and that the explosions rang out only after they had yelled "Run out!" to the hostages.

Basayev's e-mail offered new details of the siege, saying the 33 attackers included 10 Chechen men, two Chechen women, nine Ingush, three ethnic Russians, two Arabs, and five other Russian citizens from various ethnic groups. Russian authorities have said there were 32 attackers, all but one of whom had been killed. One was captured.

The e-mail said Basayev had personally trained the attackers for 10 days in a forest about 12 miles from Beslan. He denied reports that some of the fighters objected when they found out children would be among the hostages.

The e-mail outlined what the demands had been: If the president decreed an end to fighting, the return of troops to their barracks and a troop withdrawal, the attackers promised they would give the hostages water; if the troops were really withdrawn, they would have given them food.

"As soon as the troops are withdrawn from the mountains, we will let children up to age 10 go, the rest after the full troop withdrawal," it said of the demands.

If Putin had resigned, the attackers would have freed all the children and left for Chechnya with the remainder of the hostages, the e-mail said.

It denied Russian charges that he receives money from Al Qaeda leader Usama bin Laden, and said he had received less than $20,000 from abroad this year.

"I am not acquainted with bin Laden," Basayev said. "I don't receive money from him but would not refuse it."

The letter appealed to the world to recognize the righteousness of the Chechen independence fight.

"We regret what happened in Beslan. It's simply that the war, which Putin declared on us five years ago, which has destroyed more than 40,000 Chechen children and crippled more than 5,000 of them, has gone back to where it started from," Basayev wrote.

Casualty figures in Chechnya vary widely, though many estimates say about 80,000 civilians — 40 percent of them children — died in the first Chechen war. Countless more have been killed since the conflict exploded again in 1999.

In an article published Friday, meanwhile, former President Boris Yeltsin expressed concern over Putin's proposed political reforms, voicing rare public criticism of the man he promoted.

Under Putin's plan, governors would no longer be elected by popular vote, and parliament would be elected solely on the basis of party lists, not in district races. Officials have tried to justify the reforms by saying they would boost Russian unity and mobilize the nation against terrorism.

Yeltsin said in the weekly Moskovskiye Novosti that while "tough and quick" action is needed, he warned that curtailing democracy would help the terrorists.

"We will not allow ourselves to deviate from the letter and, above all, the spirit of the Constitution ... if only because the stifling of freedoms, and curtailment of democratic rights would be, among other things, a victory for terrorists," Yeltsin wrote.

Former Soviet leader Mikhail Gorbachev, whose liberal reforms paved the way for the Soviet collapse and Yeltsin's ascent, leveled harsh criticism at Putin's initiatives.

"Under the motto of fighting terrorism, it is proposed to sharply restrict democratic freedoms and deprive the citizens [of the right] to directly express their attitude toward the authorities in free elections," Gorbachev wrote in the same newspaper.