MOSCOW (AP) _ Six suspects have been charged in connection with deadly apartment building bombings in Moscow and two other Russian cities this fall, officials with Russia's Federal Security Service said Thursday.

The explosions, which killed some 300 people and shocked Russia, have been blamed on rebels from breakaway Chechnya. They helped trigger the Russian military offensive in the republic.

High-ranking Federal Security Service officials did not identify five of the six suspects Thursday. But they reiterated their claim that the bombings have been traced to Chechnya.

The explosives used in the blasts were produced in the Chechen city of Urus-Martan, Nikolai Sapozhkov, deputy chief of the agency's investigations division, told a news conference. He said a cache of the same type of explosives was discovered after the city fell under Russia control during the current Chechnya war.

Five of the six suspects have been charged in absentia, Sapozhkov was quoted as saying by Russian news reports. The sixth suspect, identified as Ruslan Magayayev, is being held in Moscow's Lefortovo prison, he said.

Another senior FSB official, Alexander Shagako, told the news conference that the secret service had prevented at least six other major terrorist attacks in Moscow, the ITAR-Tass news agency reported.

Some Russian media have speculated that the bombings were arranged by the FSB itself to ensure public support for the Chechnya war. Russia's acting President, Vladimir Putin, dismissed the allegations as ``delirious nonsense'' in an interview last week.

Putin is widely popular because of his tough handling of the Chechnya offensive and is seen as a shoo-in in Russia's March 26 presidential election.