The Taliban lured US forces into an elaborate trap to shoot down their helicopter, killing 30 American troops in the deadliest such incident of the war, an Afghan official said on Monday.
A total of 38 people -- 30 US troops, many of them special forces, plus seven Afghan commandos and an interpreter -- were killed when their Chinook came down during an anti-Taliban operation late Friday.
The crash marked the biggest single loss of life for American and Nato forces since the US-led invasion of Afghanistan toppled the Taliban in late 2001, shortly after the September 11 attacks.
The senior government official told AFP on condition of anonymity that a Taliban commander, Qari Tahir, lured US forces to the scene by tipping them off that a Taliban meeting was taking place.
He also said four Pakistanis helped Tahir carry out the strike.
"Now it's confirmed that the helicopter was shot down and it was a trap that was set by a Taliban commander," said the official, citing intelligence gathered from the area.
"The Taliban knew which route the helicopter would take," he added.
"That's the only route, so they took position on the either side of the valley on mountains and as the helicopter approached, they attacked it with rockets and other modern weapons. It was brought down by multiple shots."
The official also said that President Hamid Karzai's US-backed government "thinks this was a retaliation attack for the killing of Osama Bin Laden."
The Taliban themselves did not make such an assertion on claiming responsibility for the attack, which took place in the Taliban-infested Sayd Abad district of Wardak province, just southwest of Kabul.
US media has reported that the dead included members of the Navy's SEAL Team Six, the secretive unit behind the daring raid that killed bin Laden in Pakistan in May.
US administration sources interviewed by AFP said the casualties did not include anyone who took part in the bin Laden raid on May 2.
A spokesman for the Nato-led International Security Assistance Force (ISAF) in Afghanistan said it was still investigating the exact circumstances of the crash when asked about the claims that it was a Taliban trap.
He said the bodies had been recovered from the site.
Afghan officials said an insurgent rocket downed the helicopter, which was said to have broken into several parts after being hit.
In eastern Afghanistan on Monday, another helicopter made a "hard landing" in Paktya province, although no one was injured, ISAF said.
"What caused the aircraft to make the hard landing is under investigation -- however initial reporting indicates there was no enemy activity in the area at the time of the incident," it added in a statement.
US President Barack Obama and his Afghan counterpart Karzai reaffirmed their commitment to the war on Sunday in a telephone call following Friday's crash, the White House said.
Karzai expressed his condolences for the "tragic loss" and Obama noted the "extraordinary service" of the Americans who died and expressed his condolences for the Afghans who died serving by their side," the White House said.
Karzai and Obama then "reaffirmed their commitment to the mission in Afghanistan, which is critical to the security of both our countries."
There are currently around 140,000 foreign soldiers in Afghanistan, including about 100,000 US troops.
All international combat troops are due to leave by the end of 2014, but intense violence in recent months, including a series of assassinations in the volatile south, has raised questions about the capability of Afghan forces.
Some foreign troop withdrawals have already begun as part of a transition that has seen local soldiers and police take control of a handful of safer areas this summer.