A blast equivalent to five kilograms of TNT exploded early Sunday near the town of Izberbash, derailing the locomotive and eight cars, transport police spokesman Akhmed Magomayev said. Another, less powerful blast aimed at killing rescuers detonated nearby shortly after the first explosion, he said.
The explosions "continued the pattern" of terrorist attacks against symbols of authority that included the November bombing of a high-speed train that killed 26 people near St. Petersburg, Magomayev said.
Two suicide bombers killed 40 rush-hour commuters on the Moscow metro last week, shocking Muscovites as terrorism returned to the capital for the first time since 2004. On Sunday, the Emergency Ministry raised the number injured in the subway bombings to 121.
The bombers, aged 17 and 20, were identified as widows of militants killed by Russian security forces last year. A Chechen militant leader claimed responsibility for the subway attacks as revenge for the Feb. 11 slaying of local garlic-pickers in a forest by Russian security forces.
Dagestan is the epicenter of almost daily violence that has plagued Russia's predominantly Muslim North Caucasus region for years following two separatist wars in neighboring Chechnya.
Prime Minister Vladimir Putin has vowed to "drag out of the sewer" the organizers of the subway bombings, and Prime Minister Dmitry Medvedev promised "crueler" measures to crack down on terrorism.
In Kostek, a poor rural village in Dagestan, the family of 17-year-old Dzhanet Abdurakhmanova, one of the accused Moscow subway bombers, said Saturday they disowned her as soon as she was abducted into marriage by a militant.
"We turned our back on her when she married that one about two years ago," said a 20-year-old man, Abdurakhmanova's cousin, who refused to give his name for fear of reprisals.
Abdurakhmanova's suicide attack has brought unwanted attention to the village. Men on the main square stare at newcomers, then turn away whispering. The village feels dangerous even for those who live in the provincial capital, just 100 kilometers away.
Two more suicide bombers killed 12 people Wednesday in the Dagestan town of Kizlyar, two militants died Thursday in an explosion in the province and a policeman was killed in a drive-by shooting there by militants on Saturday.
Human rights groups and opposition figures accuse Russian federal forces and police of extrajudicial killings, abductions and abuses in the North Caucasus that has fueled the region's fierce insurgency.