Updated 6:22 p.m. ET
Female suicide bombers blew themselves up Monday in twin attacks on Moscow subway stations packed with rush-hour passengers, killing at least 38 people and wounding more than 60, officials said. The carnage blamed on rebels from the Caucasus region follows the killings of several high-profile Islamic militant leaders there.
The blasts come six years after Islamic separatists from the southern Russian region carried out a pair of deadly Moscow subway strikes and raise concerns that the war has once again come to the capital, amid militants' warnings of a renewed determination to push their fight.
Chechen rebels claimed responsibility for a deadly bombing late last year on a passenger train en route from Moscow to St. Petersburg. Last month, Chechen rebel leader Doku Umarov warned Russians in an interview on a rebel-affiliated Web site that "the war is coming to their cities."
In October 2002, a Moscow theater audience was taken hostage and more than 100 of them died along with the rebels in the rescue attempt. In the most terrible attack, more than 300 died - most of them children - at a school siege in the North Caucasus town ofin September of 2004, CBS News correspondent Mark Phillips reports.
Those events - and most recently the bombing of a Moscow-St Petersburg train last year - are evidence that Russia's military response has not worked.
A profile of Umarov on the BBC's Web site says the powerful Chechen warlord has been accused by Russia's security forces of being behind the Beslan siege.
The rebel groups' Web sites have paraded willing women suicide bombers known as the Black Widows, Phillips reports.
President Obama called Russian President Dmitry Medvedev Monday to express condolences on behalf of the American people over the deaths and injuries from the "outrageous terrorist act" and promised that the "United States was ready to cooperate with Russia to help bring to justice those who undertook this attack," according to a White House readout of the call.
Earlier Monday, Obama condemned the bombings in a statement and called the attack "heinous."
The U.N. Security Council also condemned the attacks as "an unjustifiable crime."
The first explosion took place just before 8 a.m. at the Lubyanka station in central Moscow. The station is underneath the building that houses the main offices of the Federal Security Service, the KGB's main successor agency, a symbol of power under Vladimir Putin.
About 45 minutes later, a second explosion hit the Park Kultury station, which is near the renowned Gorky Park. In both cases, the bombs were detonated as the trains pulled into the stations and the doors were opening.
A Russian television reporter, Yulia Shapovalova, was at Park Kultury when the second bombing occurred.
"I personally saw a young woman covered with blood and another was so scared she was crying," she said. "And a third was talking on her mobile phone thanking god for her survival and after all that I realized that I had survived myself."
"I heard a bang, turned my head and smoke was everywhere. People ran for the exits screaming," said 24-year-old Alexander Vakulov, who was on a train on the platform opposite the targeted train at Park Kultury.
"I saw a dead person for the first time in my life," said Valentin Popov, 19, who had just arrived at the station from the opposite direction.
Prime Minister Putin, who built much of his political capital by directing a fierce war with Chechen separatists a decade ago, vowed Monday that "terrorists will be destroyed."
Moscow is unlikely to hit back at the rebels with massive firepower: the Kremlin has installed loyal leaders in the areas where the militants operate, making bombing campaigns of the kind used in the 1990s Chechen wars out of the question.
The Kremlin is already engaged in a huge escalation of its operations to smash the rebels, and it is difficult to see what more it could do.
The iconic Moscow subway system is the world's second-busiest after Tokyo's, carrying around 7 million passengers on an average workday, and is a key element in running the sprawling and traffic-choked city.
Russian TV showed amateur video from inside the Lubyanka station of wounded and possibly dead victims sitting and lying on the floor. The train platform was filled with smoke. The LifeNews.ru site showed gruesome photos of dead passengers sprawled inside a mangled subway car and a bloody leg lying on a station platform.
CBS News' Svetlana Berdnikova reports that police stepped up patrols around Moscow's subway stations following Monday's attacks, including stop-and-search checks of random civilians.
Monday's blasts revived anti-Muslim sentiments in Moscow, aimed primarily at migrants from the former Soviet republics, says Berdnikova.
The last confirmed terrorist attack in Moscow was in August 2004, when a suicide bomber blew herself up outside a subway station, killing 10 people. Responsibility for that blast was claimed by Chechen rebels.
A more devastating attack took place in February of that year, when a suicide bomber from the North Caucasus set off explosives during morning rush hour as it traveled between stations. More than 40 people were killed and more than 100 wounded.
Russian police have killed several Islamic militant leaders in the North Caucasus recently, including one last week in the Kabardino-Balkariya region, which have raised fears of retaliatory strikes by the militants.
The militants receive moral and perhaps financial support from al Qaeda. Dozens of contributors to three Web sites affiliated with al Qaeda wrote comments in praise of Monday's attacks.
One site opened a special page to "receive congratulations" for the Chechen rebels who "started the dark tunnel attacks in the apostate countries," and all wished for God to accept the two sisters as martyrs.
"Don't forget Russia's crimes of genocide in the Caucasus and Chechnya," said one writer. "The battle has been shifted to the heart of Moscow," another wrote.
In a televised meeting with President Dmitry Medvedev, Federal Security Service head Alexander Bortnikov said body fragments of the two bombers pointed to a Caucasus connection. The bombers have not been identified and Bortnikov did not elaborate.
"We will continue the fight against terrorism unswervingly and to the end," Medvedev said.
Neither he nor Putin, who was on an official trip in Siberia, announced specific measures and it was not clear if Russia has new strategies to unleash in the Caucasus, where violent separatism has spread from Chechnya into neighboring republics.
Although the Russian army battered Chechen rebels in massive assaults a decade ago, the separatists continue to move through the region's mountains and forests with comparative ease and launch frequent small attacks.
"It's the same old answers that we have heard before about smashing terrorists, eliminating them, leaving no-one unpunished," Jonathan Eyal an analyst at Britain's Royal United Services Institute told Phillips. "Arguments that are kind of understandable in the level of frustration at the moment but do nothing in the long term."
as a precaution following the Moscow bombings. A spokesman for New York's Metropolitan Transportation Authority, Kevin Ortiz, said the agency has a "heightened security presence," but declined further comment.
The agency is in charge of New York City buses and subways, as well as suburban trains, and bridges and tunnels. In London and Madrid, two other cities that have suffered transit system terror attacks, officials said there were no immediate plans to tighten security.
At 4 p.m., the two Moscow subway stations reopened and dozens boarded the waiting trains.
"It's really terrifying," said Vasily Vlastinin, 16. "It's become dangerous to ride the metro, but I'll keep taking the metro. You have to get to school, to college, to work somehow."
Both stations had been scrubbed clean. Holes left by shrapnel in the granite were the only reminder of the day's tragic bombings.