The joint forces carried out the nighttime operation in the Zhari district of Kandahar, said provincial governor Asadullah Khalid. Four other suspected militants were arrested. There were no casualties among Afghan or NATO forces, he said.
NATO spokesman Maj. John Thomas said the military used airstrikes in the operation around daybreak Tuesday, and that it was possible a "small number of insurgents" were killed. Wounded militants were provided with medical care, he said.
Zhari was the site of one of NATO's largest-ever operations last fall and remains a volatile area. Seven Afghan police died in a roadside bomb explosion in Zhari on Monday.
Southern Afghanistan has seen fierce fighting in the last several weeks. More than 2,900 people — mostly militants — have been killed in insurgency-related violence in Afghanistan this year, according to an Associated Press tally of numbers provided by Western and Afghan officials.
Police in Kabul, meanwhile, detained a man from Saudi Arabia whom they accused of planning suicide attacks against high-ranking government officials.
The 35-year old man, identified as Yousuf Ibrahim, from Saudi Arabia's capital of Riyadh, was detained after a brief scuffle with police in the capital on Tuesday, said Gen. Ali Shah Paktiawal, the head of criminal investigations for Kabul.
Ibrahim, who was brought handcuffed in front of reporters, had spent the last eight years in Afghanistan, fighting alongside the Taliban in Kandahar, Paktiawal said.
Ibrahim, speaking in Arabic, said he was not in Afghanistan to fight against the government.
"We are here to fight against the Russians, Americans, Jews and infidels," he said, while seated on a chair in Paktiawal's office. "I am a mujahedeen (holy warrior) ... and I will fight against them until the end of the earth."
Elsewhere, U.S.-led coalition troops killed a suspected militant and detained two others during an operation in eastern Afghanistan Tuesday, officials said.
The suspected militant was shot as coalition troops were entering a compound suspected of housing militants in the Zana Khan district of Ghazni province, a coalition statement said.
In neighboring Zabul province, Taliban militants ambushed a police patrol Monday in the Mizan district, killing one policeman, said Ali Khail, spokesman for the Zabul governor.
A 30-minute gun battle ensued, leaving three suspected Taliban dead, he said.