国际英语新闻：Medvedev vows to fight terrorism following Moscow metro blasts

Head of Russia's Federal Security Service (FSB) Alexander Bortnikov said the bombers were linked to groups in North Caucasus.

"According to preliminary information, these terrorist acts were committed by terrorist groups related to the North Caucasus Region. We'll consider it as the basic version because the bodies of two female suicide bombers who were residing in the North Caucasus have been found (at the explosion sites)," the FSB chief said.

The first blast occurred in the busy central Lubyanka station, just beneath the FSB headquarter and 500 meters from the Kremlin.

A police source earlier told the RIA Novosti news agency that an inspection of the scene indicated that the bomb was detonated at a height of one to two meters, which would "apparently be attached to the waist of a female suicide bomber."

Close circuit TV showed two other women accompanied the suicide bombers onto the metro, reported Russia Today TV station.

Oleg Yelnikov, spokesman of the Russian Interior Ministry, said on TV Monday that 700 interior troops were patrolling the streets and a massive police operation has been launched in Moscow.