A U.S. soldier was taken into custody after an Afghan detainee was found dead in his cell, apparently from a gunshot wound, NATO said in a statement Tuesday night.
The man was found dead in his holding cell in Kandahar province's Arghandab district on Sunday. He was being held temporarily at an Afghan government facility under U.S. guard, awaiting transfer to coalition custody.
The U.S. has launched a criminal investigation into the death, NATO said. Rear Adm. Greg Smith said the U.S. takes seriously any allegations of mistreatment of prisoners.
Also in southern Afghanistan, militant attacks killed three NATO service members on Tuesday, the international coalition said.
NATO did not give the nationality of the dead service members or provide exact locations of the attacks. One was killed in an insurgent attack and two others by roadside bombs.
Violence in southern Afghanistan has risen in recent months as NATO and Afghan forces try to seize control of the Taliban stronghold of Kandahar. This year has been the deadliest for international forces in the nine-year Afghan conflict. At least 47 NATO service members have been killed so far this month, and more than 2,000 have died since the 2001 U.S.-led invasion.
Four Taliban commanders were also reported killed in three separate incidents.
A NATO airstrike killed one Taliban leader in Nad Ali district in southern Helmand province on Monday, the Helmand governor's office said.
Another airstrike killed 15 insurgents on Sunday, including a senior Taliban military leader for Dahana-i-ghuri and Pul-e-khumri districts in Baghlan province, NATO said. A second insurgent leader from the same province was also killed in the same attack.
Another midlevel Taliban commander was killed Sunday by NATO forces in the Pech River Valley in Kunar province near the Pakistan border, the alliance said. The commander was accused of organizing kidnappings, helping Arab and Pakistani fighters cross the border and attacking NATO convoys.
In southern Kandahar province, the coalition said 10 insurgents were reported killed and several more detained after they fired on a joint NATO and Afghan army patrol on Monday.
In a separate development, 40 Taliban fighters deserted to the government in northern Kunduz province on Sunday, deputy governor Amdullah Danishi said on Tuesday.
There are several programs running to reintegrate Taliban fighters but men who previously defected complained they were not provided with jobs or alternative livelihoods. A new government program aims to address those problems.
The violence follows last month's parliamentary elections _ tainted by allegations of fraud _ and comes amid a diplomatic push to open formal negotiations between the Afghan government and factions of the insurgency.
President Barack Obama has said he wants to begin drawing down American troops by next summer, but it is unclear whether Afghanistan's poorly paid and badly trained security forces will be able to take over.
Insurgents have increased attacks across the country in recent months despite a push against their strongholds in the south, and the Afghan government remains weak, corrupt and unpopular with many of its citizens.