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

Afghan police arrested three men for the shooting death of an Afghan Red Crescent official in northern Afghanistan. The shooting Friday was an apparent attempt to settle a long-standing dispute.

In the prison escape, the inmates 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 prison in Kabul, inmates 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.

Police detained a father, his son and a nephew in northern Takhar province Friday, provincial police chief Gen. Ziauddin Mohmoodi said.

They attacked the victim -- the Afghan Red Crescent 's provincial chief who goes by the single name Abdullah -- after he left a mosque where he attended Friday prayers.

Mohmoodi said he did not believe the killing had anything to do with his work with the aid group, but did not provide further details.

Abdul Rahman Kalantari, an official with the Afghan Red Crescent in Kabul, said Abdullah was targeted because of a private feud with his attackers.

President Hamid Karzai condemned the killing in a statement released Saturday.

Also Saturday, a bomb exploded in a large trash container in the centre 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 neighbourhood close to the U.S. 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.