Three U.S. soldiers and three Afghan civilians were killed by a suicide car bomber Tuesday in eastern Afghanistan’s Kapisa province, according to wire reports.

Pro-Taliban insurgent leader Gulbuddin Hekmatyar’s Hezb-e-Islami organization claimed responsibility for the suicide car bomb attack on a military convoy. Waliullah, a spokesman for Hekmatyar, told wire services that the attack in the northern Sayat district killed the commander of the U.S. military’s provincial reconstruction team in Kapisa province.

Waliullah’s claims could not be confirmed.

A suicide bomber in a Toyota Corolla smashed into the military convoy outside the provincial capital, Abdul Halim Ayar, a spokesman for Kapisa’s governor, told The Associated Press.

Tech. Sgt. Chuck Marsh, a U.S. military spokesman, told The AP another U.S. servicemember was wounded in the attack. The soldiers served with NATO’s International Security Assistance Force.

Two Afghan civilians also were wounded, the Interior Ministry said in a statement according to The AP.

Col. Greg Julian, the head U.S. military spokesman in Afghanistan, said there were American casualties but did not have further details on the incident or whether a PRT leader was killed.

Kapisa was once a hotbed of the insurgency, but coalition efforts there this year have been aimed at taking back key areas from insurgents, flooding them with infrastructure projects to maintain support. However, this progress was largely made before the traditional summer fighting season kicked off.

Bomb attacks will rise 50 percent this year to 5,700 — up from 3,800 last year, U.S. military officials predict.

According to military figures, 172 coalition forces were killed in such attacks last year — and far more Afghan civilians died.

Taliban forces regularly use suicide attackers and roadside bombs in assaults on foreign and Afghan troops across the country. Such attacks were up 25 percent the first four months of 2009 compared with the same period last year, The AP reported.