Chechnya: Round two? Battle for the Caucasus Cat-and-mouse conflict Islamic roots in Dagestan Russia's demoralised army

Dagestan's Interior Ministry said 2000 Islamic fighters crossed from neighbouring Chechnya early on Sunday, and seized several villages in Novolakskiy District.

But officials with the Russian forces who have been fighting the separatist rebellion since last month, put the rebel forces at no more than 300.

Russian officials have also linked Islamic militants to an explosion on Saturday in an apartment building used by soldiers' families, in which at least 20 people were killed.

The BBC's Paul Anderson: "The rebels violent campaign is gathering pace"

Chechnya, where Islamists have seized effective control of the government, has provided a base for rebels who last month declared an Islamic republic in part of Dagestan.

Blast destroys flats

At least 20 people were killed and some 70 injured in the explosion in the town of Buinaksk. No group has admitted responsibility for the attack.

Rescue workers search for people in the rubble

But Russian authorities blamed it on Islamic militants and opened a criminal investigation into what they called a "terrorist" attack.

"The explosion at Buinaksk and the incursion from Chechnya are links in the same chain," said Deputy Interior Minister Vladimir Kolesnikov.

The BBC's Andrew Harding reports: "The Russian authorities blame Islamic extremists for the attack"

The apartment block contained 25 flats. Two houses adjoining the building were also destroyed, the Itar-Tass news agency said.

It said a crater was found next to the building, and a car packed with explosives defused in another part of the town.

The incident occurred at 2200 local time (1800 GMT) on Saturday.

Reports said that Russian jets bombed two villages occupied by the rebels near Buinaksk on Sunday.

Garrison town

In recent months, the town has been flooded with Russian troops sent in to crush the separatist Islamic rebellion.

Buinaksk lies on the edge of the Caucasus mountain range - only a few miles away from Chechnya.

After several weeks of pitched battles and dozens of casualties, Russian forces appear to be gaining the upper hand, but the security situation remains extremely tense.