Some 500 Taliban prisoners escaped from an Afghan prison overnight through a massive underground tunnel that inmates had secretly created, officials said Monday.

The Taliban said it was behind the operation in Kandahar, the militant Islamist organization’s heartland in the south of the country, and that all of those who escaped were its members, many of them senior commanders, according to Agence-France Presse.

Taliban insurgents dug a tunnel more than 1,050-feet (320-meters.) The tunnel went from the main jail in Kandahar city to a house in the vicinity. Some 541 prisoners escaped, 106 among them were Taliban fighters, according to Al Arabiya correspondent Baker Atyani.

An official from Taliban told Al Arabiya the plan has been set five months ago.

The Taliban official told Al Arabiya, many buses were waiting for the prisoners at the end of the tunnel and they were transported to safe locations controlled by Taliban.

It was the second high-profile escape from the prison in three years, and is likely to be seen as yet more evidence of the country’s chaotic justice system. The episode certainly constitutes an embarrassment for local security forces.