Muhammad Yunus, former chief of the ousted Taliban's customs department at Kabul airport, has been handed over to US forces, an Afghan official said on Sunday.
Yunus was captured from his home in Nawzad district in the southern province of Helmand during a raid on Saturday, Helmand's intelligence chief, Dad Muhammad Khan, said.
"We then handed him over to the Americans who had requested it," Khan added.
"We suspect that Yunus has been leading the attacks in various parts of Helmand. But we have to prove that and it is too early to say anything as the Americans have not finished questioning him."
The arrest came amid continuing clashes in southern Afghanistan. Up to nine government troops died when they were attacked at a security post 140 kilometres north east of the southern city of Kandahar.
The ambush, by about 20 Taliban fighters, took the government troops by surprise and they were unable to react, said Fazaluddin Agha, chief of administration in the nearby district of Spin Boldak.
Government sources put the toll at five but Taliban commander Mulla Rahmat Allah told Reuters that all nine Afghan soldiers at the post were killed.
In the other incident two government soldiers lost their lives when their vehicle was blown up by a remote-controlled device as it travelled with a convoy along the road linking Khost in the east to the capital Kabul.
The road had been used earlier in the day by members of the 12,000 strong US force earlier in the day, witnesses said.
Over 400 killed
Several Afghan soldiers and local aid workers have been killed in attacks in the past five months in Helmand.
Helmand was once a stronghold of the Taliban militia, overthrown by US-led forces in 2001 for harbouring Usama bin Ladin and his al-Qaida network.
The attacks in Helmand are part of a wave of violence in Afghanistan in which more than 400 people, including civilians, aid workers, rebels, Afghan soldiers and more than a dozen coalition troops have been killed.
Some of the arrested fighters are in American custody in Afghanistan while others are being held in Guantanamo Bay, the military base of the US in Cuba.
In a separate incident, several civilians were injured when an explosive device went off near a hotel outside the eastern city of Jalalabad on Friday night, officials said, blaming rebels for the attack.