KABUL, Afghanistan - Two roadside bombs killed 19 people and wounded four Friday in Afghanistan as civilians are increasingly being caught in crossfire of the fighting between the Taliban and the U.S.-led coalition.

A minibus ran over a bomb in Nahri Sarraj district of Helmand province, with the blast killing all 18 passengers, said Kamaluddin Sherzai, the province's deputy police chief.

"The mine was very powerful and destroyed the vehicle," he said. "They were all civilians. Some were children."

Another civilian was killed and four were wounded when the farm tractor they were riding in struck a mine in Garmser district, Sherzai added.

Police who responded to the minibus explosion came under fire from insurgents, but there were no casualties among the policemen.

However, Sherzai said three Afghan policemen died in a fight with insurgents Thursday night in Helmand's Gereshk district.

In its midyear report, the United Nations said the number of Afghan civilians killed in war-related violence rose by 15 per cent in the first half of 2011.

The report said 1,462 Afghan civilians lost their lives, including 444 killed by roadside bombs. During the first half of last year, 1,271 Afghan civilians were killed in the war.

Violence has been on the rise as insurgents try to regain territory lost last fall and winter to the U.S.-led coalition in southern Afghanistan. Suicide attacks and other bombings have intensified, with militants trying to undermine confidence in the Afghan government's ability to provide security as U.S. and other coalition combat forces start to withdraw.

In eastern Afghanistan, NATO said a security force led by Afghan troops freed a family that was taken hostage by insurgents in Dila district of Paktika province.

Insurgents captured the family on Thursday while they were fighting with Afghan and NATO troops who were searching for a local leader of the Haqqani network, which is affiliated with the Taliban and al Qaeda. Several insurgents were killed in the fighting, but the family was not harmed, the coalition said.

Also in the east, a Taliban leader disguised as a woman was killed Thursday after he tried to attack an Afghan-led security force in Baraki Barak district of Logar province.

The leader was hiding under a burqa, a long, all-encompassing garment worn by some Afghan women, when he was spotted by pro-government troops. He was killed after he fled to a nearby tent and tried to get a weapon to attack the troops.