TALOOQAN: An apparent air strike by foreign forces killed 10 election campaign workers in Afghanistan`s north on Thursday, a government spokesman said, and NATO-led forces said they were investigating the incident.

Civilian casualties caused by foreign forces while hunting militants have been a major source of tension between President Hamid Karzai and Western nations.

Violence across Afghanistan is at its worst since the Taliban were ousted in late 2001, despite the presence of almost 150,000 foreign troops, with civilians bearing the brunt.

Thursday`s attack happened in the Rostaq district of Takhar, a relatively peaceful province in the north near Tajikistan, said a spokesman for the provincial governor, unlike areas in the south and east where the resurgent Taliban are mostly active.

Spokesman Faiz Mohammad Tawhidi said the candidate, Abdul Wahid, and some of his supporters were wounded in the air strike, which Tawhidi said included two helicopters and two fixed-wing aircraft.

Tawhidi initially said six people were killed but later said the toll had risen to 10. He said he had been told of the strikes by security officials.

A spokesman for the NATO-led International Security Assistance Force (ISAF) said investigations were under way.

"We are now aware of the allegations and we`re looking into the operations taking place in the area," the spokesman said.

There are no foreign troops stationed in Takhar, according to an ISAF troop distribution map, (www.isaf.nato.int), but German units are based in Kunduz to the west and Badakhshan to the east.

Last September, a U.S. air strike called in by German troops killed scores of people in Kunduz, at least 30 of them civilians. The strike led to the resignation of the German defense minister.

In the southeast, Afghan and coalition troops fought off an attack on a combat outpost in the Bermel district of Paktika province near the border with Pakistan, killing at least 20 insurgents in air strikes, ISAF said.

Last Saturday, more than 30 insurgents were killed when they launched brazen pre-dawn raids on two foreign bases in eastern Khost province. No ISAF troops were killed in either incident.

Foreign military deaths in Afghanistan have reached record levels this year, with at least 490 killed so far this year compared with 521 in all of 2009, according to monitoring website www.iCasualties.org and figures compiled by Reuters.

Increased violence is already threatening security for the September 18 parliamentary poll, with four candidates and up to 13 campaign workers and supporters killed by suspected insurgents in recent weeks.

Last month, a United Nations report said civilian casualties had risen by 31 percent in the first six months of 2010 compared with the same period last year, with more than three-quarters of them caused by insurgents.

The number caused by "pro-government forces" dropped dramatically, the U.N. report said, mainly because of a reduction in those caused by aerial strikes after commanders tightened engagement rules.

Foreign troops under the command of NATO and the U.S. military have become more active in the north after insurgents opened pockets of resistance in the past year.

The September 18 election is seen as a crucial test of stability for Afghanistan and for the U.S.-led Afghan war ahead of President Barack Obama`s strategy review in December.

BDST: 1700 HRS, September 2, 2010