Taliban insurgents dug a more than 320-metre tunnel underground and into the main jail in Kandahar city and whisked out more than 450 prisoners, most of whom were Taliban fighters, officials and the insurgents said Monday.

Kandahar city, in particular, has been a focus of the international effort to establish a strong Afghan government presence in former Taliban strongholds. The 1,200-inmate Sarposa Prison has been part of that plan. The facility has undergone security upgrades and tightened procedures following a brazen 2008 Taliban attack that freed 900 prisoners. Afghan government officials and their NATO backers have regularly said that the prison has vastly improved security since that attack.

Taliban spokesman Zabiullah Mujahid said insurgents on the outside dug the tunnel to the prison over five months, bypassing government checkpoints and major roads. The tunnel finally reached the prison cells Sunday night, and the inmates were ushered through it to freedom by three prisoners who had been informed of the plan, Mujahid said.