KABUL: Twenty Afghan civilians including women and children were killed in a volatile southwestern province Thursday when a landmine exploded under a bus they were travelling in, police said.

“An IED (improvised explosive device) struck a bus, 20 civilians were killed,” said senior police figure Haji Mosa Rasooli, accusing the Taliban of being responsible for the blast.

The Islamist militants, who have been waging a near decade long insurgency against the Afghan government and foreign forces, were not immediately available for comment.

The blast occurred in the remote Nimroz province at around 4:00pm (1130 GMT) in the region's Khash Rod district on the main highway to Kandahar, the de facto capital of southern Afghanistan.

The incident came on the same day as a father, a mother and their four children were killed in southern Afghanistan when a roadside bomb ripped through their car.

The family were travelling to Lashkar Gah, the main town in Helmand province, when they were killed, provincial spokesman Daud Ahmadi said.

Although the attack bore the hallmarks of the Taliban, who frequently plant roadside bombs in Afghanistan's restive regions, the militant Islamist network declined to comment on the attack.

Civilians are the biggest casualties in the near 10-year war in Afghanistan, where 150,000 foreign forces are stationed.

Last year was the bloodiest yet for civilians, with the United Nations recording 2,777 fatalities?

A total of 368 civilians were killed in May alone according to figures released by the UN mission in Afghanistan, with insurgent attacks blamed for 301 of those.

The latest civilian deaths are a reminder of the depth of the task facing the Afghan government as it takes increasing responsibility for security following the announcement of the first wave of foreign troop withdrawals.

The drawdown, which will start in July, will include the departure of 10,000 US troops this year despite questions from analysts over whether Afghan security forces can cope in their absence.

The UN has blamed insurgents for more than three-quarters of the civilian deaths last year.

Civilian casualties have long been a bone of contention between successive US administrations and Afghan President Hamid Karzai, who is struggling to win the hearts and minds of Afghans and deprive the Taliban of propaganda victories.

In early June he issued a “last warning” to the US military to avoid “arbitrary and unnecessary” operations that kill civilians, after he said 14 people died in an air strike in Helmand province.

US President Barack Obama apologised for that incident, which the Nato-led International Security Force (ISAF) said killed nine civlians.