Militants from neighboring Chechnya seized three villages and a town Sunday inside the Russian region of Dagestan hours after a bomb destroyed a Russian officers' apartment building, killing 30 and injuring more than 110.
The bomb at Buynaksk, Dagestan's second-largest city, was one of three apparently designed to detonate in succession, officials said, but police managed to defuse the other two minutes before they were to go off.
The developments posed a serious new challenge to the Russian military, which only last week took credit for defeating the militants in an earlier confrontation.
In the latest assault, hundreds of fighters from Chechnya crossed into Dagestan southwest of Khasavyurt, a major provincial town that has a mix of ethnic groups, including Chechens.
Estimates of the Chechen fighters' strength ranged from 500 to 2,000 troops. Sunday night, Russian officials said the Chechens had trapped about 40 Dagestani interior troops, who were said to be running out of ammunition, inside their building, and Russian army forces could not rescue them.
Leading the incursion was Shamil Basayev, one of the leaders of the Chechen secession battle against Russia from 1994 to 1996, Russian news reports said. Basayev surprised Russian troops a few weeks ago with a cross-border campaign into Dagestan, seizing several villages and saying his goal was nothing less than creation of an Islamic republic there.
After heavy losses on both sides, the Russian military forced Basayev to retreat into Chechnya. Now, he appears to have returned with a similar tactic farther north in a border region that has often been tense. Hundreds of residents of Khasavyurt and surrounding villages were fleeing along country roads to escape the fighting.
According to Russian officials, the Chechen fighters Sunday seized the villages of Shushiya, Akhar and Gamiyakh, while a large contingent took the town of Novolakskoye, where the interior troops are trapped. Intense battles were under way late Sunday between Russian troops and the fighters.
Vladimir Kolesnikov, Russian first deputy interior minister, called the bombing and the Chechen incursion "links in the same chain." No one, however, claimed responsibility for the bombing.
The blast collapsed two sections of a five-story apartment building, which housed officers of an army brigade and their families, and took the lives of many women and children. The blast also left a crater nine feet deep. The building is located in the town of Buynaksk, not far from where Russian troops have been attacking two militant-controlled villages.
Sunday, as rescue workers struggled to pull victims from the collapsed concrete prefab building, a second bomb carrying 2,200 pounds of TNT was found, the ITAR-Tass news agency said. Parked between a military hospital and an apartment house, the truck was spotted by a sentry, and the bomb disarmed. No details were available on the disarming of the second bomb.
Both Chechnya and Dagestan are largely Muslim. Unlike Chechnya, however, Dagestan is a patchwork of dozens of competing ethnic groups, many with their own languages, and most remain loyal to Russia.
The most militant group in Dagestan is the multiethnic Wahhabi sect, which has its stronghold in the villages of Karamakhi and Chabanmakhi, about 30 miles south of Makhachkala, the capital. About two years ago, members of the sect declared the two villages to be an Islamic state and expelled Russian police.