Canadian Armed Forces Station in Afghanistan

A hunt is under way for more than 870 prisoners who escaped from a jail in southern Afghanistan after Taliban fighters blew it open, killing 15 security guards.

The Taliban claimed 400 fighters escaped after the raid in the city of Kandahar late on Friday.

A suicide-bomb blast preceded a fierce gun attack on the prison guards.

A state of emergency has been declared in the southern Afghan province of the same name.

Mohammad Qasim Hashimzai, the Afghan deputy justice minister, said the Taliban spent two months planning the raid and it was their most sophisticated yet.

"The Afghan security forces are searching for them within the city and along the main and secondary roads."

None of the escaped inmates have been caught yet, Hashimzai said.

Large numbers of security forces, including those of from the US-trained Afghan national army, have been deployed to search vehicles, AFP reports.

General Carlos Branco, a spokesman for Nato's International Security Assistance Force (Isaf), said: "Afghanistan national security forces and Isaf forces have cordoned off the area to re-establish security and recapture the escapees."

Yousuf Ahmadi, a Taliban spokesperson, said the fighters used suicide bombers and detonated a bomb-laden water tanker as part of the attack.

"First we exploded two suicide attacks and then our mujahidin (holy warriors) riding motorcycles entered the prison and killed the remaining security guards," Ahmadi said.

"We successfully freed all prisoners, including jailed Taliban and other prisoners."

The statement, signed by Ahmadi, said the Taliban had planned the attack two months ago.

Afghan officials said seven prison guards were killed in the attack. They had earlier said bodies of 15 guards had been recovered.

Hashem Ahelbarra, Al Jazeera's correspondent in Afghanistan, quoted witnesses as saying a vehicle carrying an attacker blew up near the prison gate before other fighters joined the battle and killed the guards.

"It was a co-ordinated attack and they [Taliban fighters] got assistance from the guards within the jail," Ahelbarra said.

Mark Laity, a Nato civilian spokesman, told Al Jazeera: "The release of a significant number of Taliban members is something of a setback."

"They managed to launch this attack and they succeeded, obviously we will have to learn lessons and we'll have to check to make sure that something like this doesn’t happen again.

"It is an increased security problem, this is an extra problem for us but I don’t want to overstate it. This is a bad day but this is not a bad year," he said.

Kandahar jail was the scene of a mass hunger strike by hundreds of inmates in May, during which 47 of the prisoners sewed their lips shut after complaining they had been tortured and denied fair trials.

Prisoners, including al-Qaeda and Taliban fighters, rioted at Afghanistan's main Pul-e-Charki jail, in the capital Kabul, in February 2006, taking control of a block and leaving several people injured.