No other details about the attacks on the U.S. troops were given by NATO and the identities of those killed were not immediately released in keeping with standard procedure.
A total of 55 foreign troops have been killed in Afghanistan this month, including 35 Americans, according to a count by The Associated Press. July was the deadliest month for U.S. forces in Afghanistan since the 2001 invasion, with 66 killed.
U.S. troops make up about 100,000 of the 120,000-strong foreign military contingent in Afghanistan, most of them in the south and east where the Taliban is most deeply entrenched.
Meanwhile, a police official said the three Afghan policemen and two civilians were killed and 15 civilians wounded in Thursday evening's bombing in Kunduz province's Archi town. The blast went off as residents were shopping for bread, yogurt, fruit and other food ahead in anticipation of the breaking of the dawn-to-dusk fast observed during the Islamic holy month of Ramadan.
There was no immediate claim of responsibility for the attack, but deputy provincial police chief Abdul Rahman Aqtash said civilians appear to have been the target.
"This was a cruel act of the enemy. There was nothing to link these people to the coalition or to politics," Aqtash said.
Kunduz, about 150 miles (240 kilometers) north of the Afghan capital, Kabul, has not traditionally been a Taliban stronghold. However, the insurgents have been steadily building their presence there since about 2007, mostly among ethnic Pashtuns who are a minority in the area. Attacks on a key coalition supply line running south from Tajikistan are a constant menace, along with ambushes of German forces who help provide security.
In establishing a northern foothold, Afghan authorities believe the Taliban use veterans from southern battlefields to help organize local groups, sometimes with help from the al-Qaida-linked Islamic Movement of Uzbekistan, which provides recruits from among the Uzbek minority.
"The situation is very bad and dangerous in Kunduz but unfortunately the security officials keep saying things are all right," Mabubullah Mabub, chairman of the Kunduz provincial council, told AP Thursday. "Over the last two years, the situation has been getting worse."
Farther east in Badakhshan province, Afghan army commandos aided by U.S. special forces discovered a major weapons cache in the remote village of Nawci on Wednesday, NATO reported. It said weapons found included 78 rockets with launchers, 47 mortar rounds, more than 9,000 rounds of ammunition, and 24 rocket-propelled grenades. All were destroyed.
The town is believed to be safe haven for Taliban fighters and drug smugglers, as well as a conduit for foreign fighters arriving from neighboring Pakistan, NATO said.
President Hamid Karzai on Thursday told a visiting U.S. Congressional delegation that the war against terrorists cannot succeed as long as the Taliban and their allies maintain sanctuaries in Pakistan.
A statement by Karzai's office said the Afghan leader told the U.S. delegation that significant progress had been made in rebuilding the country after decades of war. But he said the campaign against the Taliban and al-Qaida had faltered because of ongoing civilian casualties during NATO military operations and a lack of focus on "destroying the terrorists' refuge" across the border.
Karzai also said President Barack Obama's announcement that he would begin withdrawing U.S. forces from Afghanistan in July 2011 has given "the enemy a morale boost" because they believe they can simply hold out until the Americans leave.
Associated Press writer Amir Shah contributed to this report.