Taliban fighters have freed 14 inmates from a jail in western Afghanistan after staging a daring prison break, police have said.

Mohammad Faqir Askar, a provincial police chief, said the fighters blew up the main gates of the prison in Farah city after planting a bomb on Sunday.

"Twenty prisoners escaped but we arrested six of them soon after the incident and 14 are still at large," Askar said.

He said four other inmates had been injured in the blast at the facility where at least 400 prisoners are currently being jailed.

Askar blamed the blast on Taliban fighters who have been waging a bloody insurgency since they were ousted from power during the US-led invasion nearly nine years ago.

Suicide attack

In November 2009, 13 prisoners escaped from the same prison via a tunnel and in June earlier that year, at least to 1,000 Taliban inmates escaped from Sarpoza prison in Kandahar city after a suicide attack blew open the front gates and destroyed the walls.

Sunday's prison break comes just two days before Afghanistan is due to host a major international donors conference, set to be attended by up to 40 foreign ministers, including US secretary of state Hillary Clinton.

But Zemarai Bashary, a spokesman for the interior ministry, said thousands of police officers, soldiers and intelligence agents had been deployed "in vulnerable areas" of the Afghan capital, Kabul, as well as remote villages to thwart any Taliban attack plans.