After a lull of several years, the spectre of militant attacks has returned to haunt Moscow and fuelled fears of a holy war in the heart of Russia by Islamist rebels from its Northern Caucasus region.
Thirty-six people were killed Monday in twin suicide attacks carried out by female suicide bombers in the morning rush hour, officials said, in the worst such attack in the Russian capital for over half a decade.
The head of the Federal Security Service Alexander Bortnikov said they appeared linked to Northern Caucasus militant groups who have waged an insurgency against the pro-Kremlin local authorities in the last years.
The bombings came after warnings published on militant websites by Islamist leader Doku Umarov from the Caucasus region of Chechnya that Moscow would be the rebels' next target.
Andrei Malashenko, an expert at the Carnegie Centre, said the bombings could signal the beginning of a jihad, or holy war in the heart of Russia.
"I would not rule out that they have started the jihad that they have been announcing recently quite regularly since the
end of December," Malashenko told AFP.
The US IntelCenter organisation -- which monitors statements by militant groups -- also pointed to Umarov's involvement.
"The most likely group behind the twin suicide bombings in the Moscow subway today is the Caucasus Emirate led by Doku
Umarov," the agency said in a statement.
In an interview published February 14 on the Kavkazcenter website, an unofficial mouthpiece for rebels, Umarov warned that rebels would move their actitivites from the Caucasus to central Russia.
"The blood will not just be spilled in our towns and villages. The war will come to their towns," Umarov said.
Amid a low-level insurgency in the North Caucasus, rebels regularly target police stations and local officials in shootings
and suicide bombings that are barely mentioned by Russian state media.
"This is directly linked to the situation in the North Caucaus," Grigory Shvedov, the chief editor of the web site www.caucasianknot.info, told AFP.
"Human rights are being abused as before and the mobilisation base for terrorist acts is growing," Shvedov said. "We have reason to expect more terrorist acts in the future."
The Kremlin attempted to strengthen its hold in the region in January appointed a powerful new envoy responsible for the North Caucasus, Alexander Khloponin.
Medvedev called for Khloponin, who was also appointed a vice prime-minister, to concentrate on improving the economy in the region, where corruption and unemployment are rife.
Umarov had claimed responsibility for a bomb that exploded on the Nevsky Express high-speed train in November, killing 27 people and injuring around 100.
The choice of Lubyanka metro station for one of the blasts suggests that FSB workers were targeted, Malashenko added. The FSB headquarters are on Lubyanka Square.
Oleg Orlov, the leader of Memorial human rights organization, said that the attacks reflect an ongoing conflict.
"It's an armed conflict that has never stopped and the threats to transmit jihad in Russia have never stopped, Orlov said.
Analysts cited recent factors that could have precipitated the attacks as this month's announcements that Russia had killed two prominent rebel leaders loyal to Umarov, Said Buryatskay and Anzor Astemirov.
Malashenko called the latest attacks "revenge" saying that rebels realize the authorities are not ready to negotiate after the Beslan hostage crisis in 2004, when rebels seized a school in an attack that left more than 330 people dead.
"They want revenge. They can't achieve anything else. After Beslan it has become clear that the authorities will not accept negotitations with them," Malashenko said.