Taliban militants fighting Afghan and NATO-led troops surprisingly broke through to the fortified Kandahar prison and set free hundreds of inmates on Monday.

"Some 476 inmates made their escape from Kandahar jail early today," chief of Kandahar jail Ghulam Dastgir Mayar told Xinhua.

"The prisoners using underground tunnel escaped from Kandahar prison and security forces have launched a huge search operation inside Kandahar City and some districts," Kandahar provincial administration said in a statement, adding that so far some escaped inmates have been rearrested.

Some 1,000 inmates were held in Kandahar jail, according to an official who declined to give his name.

This was the fourth jailbreak in Kandahar prison over the past few years.

Meanwhile, Kandahar provincial governor Tooryali Weesa said: " Insurgents had worked for months on digging the tunnel which started in a house located to the north-east of Kandahar prison in Sarfooza area, with its entrance in the prison's political block," he said.

Qari Yusuf Ahmadi, the purported Taliban spokesman, stressed that over 500 Taliban detainees have escaped from the jail.

In talks with media via telephone from undisclosed location, he said that militants enabled 541 militants including 106 commanders to escape after digging a 360-meter long tunnel.

Kandahar, the birthplace of Taliban in southern Afghanistan, has seen rampant insurgency against Afghan security force and NATO- led foreign troops since Taliban regime was ousted in 2001.