Explosions detonated by two female suicide bombers killed at least 38 people and injured 65 on two packed Moscow metro trains in the morning rush hour on Monday, officials said.
It was the worst attack in the Russian capital for six years.
No group immediately claimed responsibility for the blasts but suspicion fell on groups from Russia's North Caucasus, where the Kremlin is fighting a growing Islamist insurgency.
Russian President Dmitry Medvedev ordered senior officials to fight terrorism "without hesitation, to the end." He said Russia will act without compromise to root out terrorists and ordered security to be boosted across the country. He said human rights must be respected during police operations, a Kremlin spokesman said.
Firefighter near Lubyanka metro station (Photo: Reuters)
Russian Prime Minister Vladimir Putin vowed to detroy those responsible for the Moscow metro suicide attacks. "A crime that is terrible in its consequences and heinous in its manner has been committed," Putin said at the start of a video conference with senior emergencies officials.
"I am confident that law enforcement bodies will spare no effort to track down and punish the criminals. Terrorists will be destroyed," said Putin, who was on a visit to the Siberian city of Krasnoyarsk.
The first blast just before 8 am (0400 GMT) tore through the second carriage of a train as it stood at the Lubyanka metro station, close to the headquarters of Russia's main domestic security service FSB. It killed at least 23 people.
Another blast about 40 minutes later wrecked the second carriage of a train waiting at the Park Kultury metro station, killing 14 more people.
"Two female terrorist suicide bombers carried out these bombings," Moscow Mayor Yuri Luzhkov told reporters at Park Kultury metro station.
Workers treat victims
Surveillance camera footage posted on the Internet showed bodies lying in Lubyanka station lobby and emergency workers treating victims.
By 0722 GMT, the rouble was 7 kopecks down at 34.20 versus the euro-dollar basket after falling to its lowest level since March 10 of 34.43 at the market opening, according to Reuters data.
2 explosions in heart of city. Moscow subway map
Sergei, a Moscow resident, told Ynet he had been on the subway when the blast occurred. "I was on the train on my way to work, and I was late. While I was travelling I heard that there had been explosions, and the train system has been disrupted. There are heavy traffic jams in central Moscow, as this is the busiest morning of the week."
The Foreign Ministry's situation room said it was unaware of any Israeli nationals hurt in the Moscow explosions, but that Israel continued to monitor the developments in Russia. "The embassy in Moscow is checking the hospitals and is in contact with the local police," said a Foreign Ministry official.
Foreign Minister Avigdor Lieberman telephoned his Russian counterpart, Sergey Lavrov and expressed Israel's condolences. Lieberman told Lavrov that "the war on terror is a global mission which must be made a top international priority, as no country is immune to the impact of dark extremists wherever they are."
US President Barack Obama condemned the bombings as did European Union leaders.
"The American people stand united with the people of Russia in opposition to violent extremism and heinous terrorist attacks that demonstrate such disregard for human life, and we condemn these outrageous acts," Obama said.
The Russian stock markets were unfazed, however, edging up in early trade.
"It is a psychological moment. The sentiment is very bad, a lot of uncertainty. The market was overshort (in foreign currencies) so the reaction is explainable," said a dealer at a major Russian bank in Moscow.
Russian prosecutors said they had opened an investigation. Russian Prime Minister Vladimir Putin was being updated regularly on developments, a spokesman said.
The current death toll makes it the worst attack on Moscow since February 2004, when a suicide bombing killed at least 39 people and wounded more than 100 on a metro train.
Chechen separatists were blamed for that attack.
Olga Gouresky and Roni Sofer contributed to this report