The blasts wrecked much of the government headquarters and dealt a severe blow to the efforts of President Vladimir Putin's government to portray the republic as returning to normal after more than three years of war between separatist guerrilla bands and a massive Russian military contingent. The government has tried to reinforce its claim by pressuring refugees to go home and shepherding foreign journalists to Grozny on carefully controlled tours to examine reconstruction projects.

There was no immediate claim of responsibility for the attack in the city of Grozny, but Russian officials variously blamed Chechnya's rebel president Aslan Maskhadov or warlord Shamil Basayev. Maskhadov broke ranks with Basayev last month after the latter claimed involvement in the October raid by Chechen gunmen on a Moscow theatre, in which 41 raiders and 129 hostages died.

A senior Maskhadov aide, Akhmed Zakayev, issued a statement from London denying involvement of Maskhadov's government. "Responsibility for the escalation of violence in Chechnya, including this act of terror, lies wholly with the Russian side," Zakayev said.

Putin in turn vowed that "No sort of terrorist crimes will break the will and aspirations of the people of Chechnya for a peaceful life," according to a statement from the presidential press service.

Viktor Shkareda, deputy head of the Emergency Situations Ministry in southern Russia, said 46 people were confirmed dead in the blast and 70 wounded. Rescuers reported finding fragments of other bodies as they scrabbled through the heaps of broken concrete and shattered glass.

Although Russian troops have had nominal control of Grozny since early 2000, the city remains largely in ruins from intense Russian air and artillery attacks. Rebels heavily infiltrate the city and bloody Russian forces there with daily hit-and-run attacks and remote-controlled explosives.

Rebels this fall also have shot down several military helicopters with shoulder-fired missiles near the main Russian base on the outskirts of Grozny. On Wednesday, gunmen shot and killed the head of a pro-Kremlin party in the city.

The explosions hit around 2:30 p.m., just after the traditional lunch break. Imran Vagapov, Chechnya's main inspector, said that the government headquarters building was full of employees and visitors. About 200 people usually worked in the building, officials said.

Among the seriously wounded were Chechen Security Council chief Rudnik Dudayev and Zina Batyzheva, a deputy prime minister, the Interfax news agency reported.

The head of the Moscow-backed Chechen administration, Akhmad Kadyrov, has offices in the building but was in Moscow at the time of the blast. Kadyrov, while increasingly critical of the Russian military campaign in Chechnya, is regarded as a turncoat by rebels, as are other Chechens who work with Russian authorities.

In Paris, meanwhile, the French Interior Ministry said a cell of suspected Islamic militants arrested this week were planning attacks against Russian interests in Chechnya and France, including the Russian Embassy in Paris.

Eight suspects were arrested in raids in Paris suburbs this week as French authorities launched an investigation into networks operating that filter extremists into Chechnya.

Initial reports said the vehicles that blew up in Grozny were a Kamaz heavy truck and a military-style UAZ light truck. The emergency ministry said the blasts' combined force was the equivalent of about a half-tonne of TNT.

The blasts left a six-metre-wide crater, destroyed one of the building's wings and left much of the main structure a shell, the emergency ministry said.

Television footage showed stunned and bleeding people stumbling out of the rubble. Others were dragged out by their hands and feet, while bloodied soldiers tried to establish order. Some 200 rescuers worked in frigid pre-dawn weather early Saturday, searching for anyone living amid the wreckage.

Kadyrov told Interfax that one of the trucks had broken through three security cordons surrounding the government headquarters. He called for an investigation of the security guards.

"How could the terrorists have managed to break through three fences around the government building? The guards' actions must be investigated," Kadyrov was quoted as saying by Interfax.

Aslan Magomadov, an envoy of Putin, said there would be "serious questions" for the Ministry of Justice, Federal Guards Service and the Federal Security Service, Interfax reported.

Soldiers sealed off the city and would keep it closed until at least Sunday, the emergency ministry said.

The largest recent attack in Grozny was in October, when rebels blew up a Grozny police precinct house, killing at least 25 people. Militants also exploded a passenger bus in September, killing 19 people, mostly civilians.

After driving rebels out of much of Chechnya in a ground campaign that began in September 1999, Russian forces have been unable to wipe them out in Grozny and rugged mountainous regions to the south of the capital. But the Russian government has insisted that Chechnya is returning to normal, and that the military campaign there is nearly complete.

"The Chechen Republic is on its way to peace and political stability as a constituent of the Russian Federation ... the scum who kill people allegedly for the sake of some ideas will never achieve anything," Chechnya's Kremlin-appointed prime minister Maikahil Babich said after the explosion.

Russian forces and Chechen rebels fought to a standstill in a 20-month war in 1994-96, after which the Russians withdrew and Maskhadov, a one-time rebel leader, became president. Under the subsequent de-facto independence, Chechnya was virtually lawless, notorious for widespread kidnappings, and Islamic fundamentalists established footholds.

Russian forces swept in again in 1999 after Chechen-based rebels raided neighbouring Dagestan and after some 300 people died in apartment bombings that officials blamed on the insurgents.