A person wearing an Afghan national security force uniform turned his weapon Sunday against civilian contractors with the U.S.-led military coalition, killing three.

In other incidents, five NATO service members were killed in roadside bombings over the past two days.

NATO said the attack on the civilian coalition workers occurred in western Afghanistan but disclosed few other details.

The gunman was killed during the incident, which is still being investigated. No further information about the civilians who died was released.

Afghan security forces or militants dressed in their uniforms have been killing a rising number of coalition forces, but they have not been specifically targeting contractors working for the coalition. So far this year, 26 foreign troops have been killed in this type of attacks.

In other violence, a spokesman for the governor of eastern Wardak province said insurgents had kidnapped five Afghan men working a base jointly operated by Afghan and NATO forces and killed them. Spokesman Shahidullah Shahid said their bodies were discovered early Sunday.

Airstrikes kill 4 civilians

Also Sunday, Afghan officials reported that four civilians died when hundreds of shells and rockets were fired from neighbouring Pakistan.

The artillery shells hit homes along frontier areas from which insurgents have in the past staged cross-border attacks.

There is little or no Afghan or NATO military presence in the area and large swaths of the region are controlled by insurgent groups. The information could not be independently verified because the area is largely off-limits to reporters.

The Afghan government has not openly blamed the Pakistani military for the artillery barrage, which reportedly hit districts in the eastern provinces of Nuristan and Kunar. Both are considered insurgent hotbeds, and militants allied with both the Afghan and Pakistani Taliban regularly cross the mountainous border in both directions.

'Rocket attacks in the eastern provinces of Afghanistan are not acceptable to us.'—Foreign Ministry Spokesman Janan Mosazai

Afghan President Hamid Karzai discussed artillery fire coming from Pakistan at a weekly meeting of his national security council, a statement said. It added that Karzai ordered an in-depth investigation into the attacks.

The cross-border attacks were discussed in Kabul last week during an official visit by Pakistan's new Prime Minister Raja Pervaiz Ashraf and British Prime Minister David Cameron.

Cameron, Ashraf and Karzai jointly called for a common stand against insurgents operating in the lawless border areas. Ashraf complained at a news conference about attacks against Pakistan originating in Kunar.

Kabul's Foreign Ministry spokesman Janan Mosazai said, "The rocket attacks in the eastern provinces of Afghanistan are not acceptable to us, and we are strongly condemning these attacks. We believe that the continuation of such rocket attacks will have a negative impact on the friendly relations between Afghanistan and Pakistan."

All five of the NATO service members were killed in roadside bomb attacks —one Saturday in the east, and on Sunday, two in the east and two in the south. NATO provided no further details on the incidents or the nationalities of the troops.

The deaths bring the number of foreign forces killed in July to 32, and a total of 247 so far this year.

NATO also said that it killed a number of insurgents with an airstrike in the Mohammad Agha district of eastern Logar province. It did not provide further details.

Fighting in eastern Afghanistan has been raging since spring as NATO tries to clear the area of insurgents.