A dozen prisoners escaped jail through a tunnel they dug from their cell to the outside in western Afghanistan, police said Saturday.

Those who escaped from Farah prison overnight included low-level Taliban militants, drug-dealers and other minor criminals, said Farah province police chief Gen. Mohammad Faqir Askar.

A 13th prisoner arrested during his attempted escape said the tunnel took 10 days to dig and the plan was to slowly empty the prison overnight, Askar said. More than 300 inmates were held in the prison, which was built to hold about 80, he said.

Afghanistan's overcrowded prisons have been plagued by problems as the country tries to establish a justice system amid ongoing conflict.

In the main jail in Kabul, prisoners took control of entire cellblocks last year before being pushed back. Taliban militants launched an assault on a prison in the southern city of Kandahar in June 2008 that freed 900 inmates.

Also Saturday, a bomb exploded in a trash bin in the center of Afghanistan's capital. Officials say the explosion did not cause any injuries or significant property damage.

Kabul police Chief Abdul Rahman Rahman says the explosion in a neighborhood close to the US Embassy did not appear to be strong.

"It was designed mostly to make a large sound, just to alarm people," Rahman said. An Associated Press reporter at the scene saw a damaged billboard but little other debris.