Updated at 7:54 a.m. Eastern.
A woman has died in a clinic from wounds suffered in the double suicide bombing of the Moscow subway, officials said Tuesday, raising the death toll to 39 as the country entered a day of mourning.
Five people remain in critical condition out of 71 hospitalized after the blasts that were blamed on Chechen rebels, city health department official Andrei Seltsovsky told the Rossiya-24 state news channel.
CBS News' David Grout reports that Muscovites continued laying flowers and photographs Tuesday at the two stations where the attacks occurred, and officials were to place memorial plaques at both stations later in the day.
Moscow's Health Commissioner said all 39 people killed in the attacks would be identified by Tuesday afternoon. Only eight victims had been formally identified as of Tuesday morning.
The preliminary investigation found that female suicide bombers detonated belts of explosives during the Monday morning rush-hour at two central Moscow subway stations.
Grout reports that Russian authorities released photos of the alleged bombers to the public, but the two women had not yet been identified.
It was the first terrorist activity in the Russian capital for years.
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, reports CBS News correspondent Mark Phillips.
According to analysts with the Washington area-based group IntelCenter, the group most likely behind Monday's blasts was the Caucasus Emirate, which had recently "demonstrated capability to conduct this type of attack and expressed intent."
IntelCenter said the group, headed by Doku Umarov, released statements in late 2009 and February of this year warning Russians that, "This war will reach the homes of each of you. It has already reached your homes. And trains that explode today are only the beginning. Planes will be blown up at your end, and war will be unleashed on your streets."
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 2004 school siege in Beslan, which resulted in hundreds of deaths.
"The Russians do not understand that the war today is coming to their streets, the war is coming to their homes, the war is coming to their cities," Umarov is quoted as saying in the statement released by IntelCenter. "They do not think that the war is coming, that it is going on only on television somewhere far away in the Caucasus and that the war does not concern them, but we plan, God willing to prove to them that the war is coming to their homes."
Flags flew at half staff on government buildings and at the Kremlin as a day of national mourning began. Entertainment events and shows on television were cancelled. Services were to be held at several churches.
Heightened transportation security remained in effect across the capital and in cities across Russia. Police with machine guns and sniffer dogs patrolled subway entrances.
Monday's first explosion took place just before 8 a.m. at the Lubyanka station in central Moscow, beneath the notorious headquarters of the Federal Security Service or FSB, the KGB's main successor agency. The FSB is a symbol of power under Prime Minister Vladimir Putin, a former KGB officer who headed the agency before his election as president in 2000.
About 45 minutes later, a second blast hit the Park Kultury station on the same subway line, 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.
Phillips reports that the two female bombers are suspected to have been "Black Widows," a group which began as the bereaved wives of Chechen men killed by Russian troops during the two wars fought over the region.
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."
Terrorism expert Steven Emerson tells "The Early Show" that the Moscow attacks likely stoked concerns that such extremism "will spill over and create copycat attacks here in the U.S."
Emerson, head of the Investigative Project on Terrorism, says U.S. government officials issued a warning just weeks ago that al Qaeda had trained a group of non-Arab women as suicide bombers. Islamic militants, says Emerson, are increasingly attempting to take advantage of women's ability to raise less suspicion among security officers, and conceal explosives in a greater variety of ways.
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.