Last updated 10:55 a.m. ET.
A U.S. military spokesman says two more U.S. troops have been killed in a blast in southern Afghanistan, bringing to six the number of Americans killed Monday.
A roadside bomb targeting an American military convoy killed four U.S. soldiers in the northern Kunduz province, said Governor Mohammad Omar.
They were involved in the training of Afghan security forces.
Omar said two Afghan civilians were also wounded in the attack in the Ali Abad district.
In comparison to the country's south and east, northern Afghanistan is relatively quiet. But roadside and other insurgent attacks have been increasing in the last few years.
Navy Chief Petty Officer Brian Naranjo said two more troops were killed in a roadside bomb attack in the country's south. He did not have further details.
Meanwhile, officials said a suicide car bomber blew himself up outside the outer gate of the main NATO base in southern Afghanistan, killing two civilians and wounding 14 other people.
Those wounded near the gates of Kandahar Airfield included 12 civilians and two Afghan soldiers, said Gen. Sher Mohammad Zazai, the top military commander for southern Afghanistan.
The incidents came as thousands of U.S. Marines in neighboring Helmand province mounted a major offensive against the Taliban. Over the weekend,
By Associated Press Writer Amir Shah; AP reporter Geir Moulson in Berlin contributed to this report