Four U.S. Marines were killed Thursday by a roadside bomb in western Afghanistan, bringing the total number of Western military deaths in August to at least 14.

NATO declined to say exactly where the Marines were killed or immediately release other details of the attack.

The military deaths came as local officials in southern Afghanistan said Thursday that roadside blasts and a U.S. air strike killed at least 15 people in the last 24 hours, including five members of a family whose tractor hit a mine on their way to a wedding party in Helmand province.

Authorities had initially reported that at least 20 people had died in a blast in the Garmser district. But Assadullah Sherzad, police chief of Helmand province, said officers on the scene have now determined that five people died.

The driver of the tractor en route to a wedding, his wife, two children and another woman died, said officials. At least two other people were injured.

"It's the work of the enemy of the nation, it's the work of the enemy of peace and the work of the Taliban," Gen. Sher Mohammad Zazai, commander of an Afghan military unit in the region, told Reuters.

Air strike kills 5: Afghan police

A police chief in a neighbouring province said a Western air strike Wednesday night killed five farmers loading cucumbers into a taxi.

The U.S. initially said the men were militants who had been seen placing weapons into a van, but said later in the day that they had been seen planting wire-controlled roadside bombs.

A UN report released last week indicated civilian deaths in Afghanistan have risen by 24 per cent during the first half of 2009 when compared with the same period last year.

The report indicated that at least 595 civilians were killed by the Taliban — mostly by suicide attack and roadside bombs — in the first six months of 2009. The report also warned that those casualties will likely rise leading into the country's presidential elections.

U.S. marines and British forces have been pushing into Helmand in an attempt to extend government control and ensure stability ahead of the Aug. 20 elections.

The Taliban have a stronghold in the region and have threatened to block roads and disrupt polls to deter voters.

With files from The Associated Press