KABUL, Afghanistan - New details that emerged Friday show that eight U.S. troops who were killed while on foot patrol in southern Afghanistan the day before were hit by two consecutive blasts, with one explosion going off as troops rushed to aid those wounded from the first blast, NATO said.

The Taliban have claimed responsibility for Thursday's attack in the southern, Kandahar province.

It was the deadliest day for NATO in Afghanistan since April 27, when a veteran Afghan military pilot killed eight U.S. troops and an American civilian contractor at Kabul airport.

The Kandahar attack started as the troops began to inspect a suspicious object they found while patrolling on foot in the mountainous Shorabak district, 12 miles (19 kilometres) from the Pakistan border. The first explosion wounded some of the service members, while the second came as others tried to help the injured, NATO said.

U.S. officials, speaking on condition of anonymity because they were not authorized to disclose the information, have confirmed that all eight victims were Americans. Two Afghan policemen also died and two others were wounded, said Gen. Abdul Raziq, chief of the Afghan border police in the province.

Separately, NATO on Friday announced the death of a service member killed in an insurgent attack, also in southern Afghanistan. Forty international service members have been killed so far this month, while so far this year, 191 coalition troops have died in Afghanistan.

Insurgents declared the start of a spring offensive on May 1 against NATO and the Afghan government.

NATO has been expecting the Taliban to stage a series of spectacular and complex attacks, and the group has already carried out a number of them recently.

The effectiveness of the Taliban's long-awaited spring campaign, code-named Badr after one of the Prophet Muhammad's decisive military victories, could affect the size of President Barack Obama's planned drawdown of U.S. troops in July.

Gen. David Petraeus, the top U.S. and NATO commander in Afghanistan, has said the size of the withdrawal will depend on conditions on the ground.

The alliance has committed itself to handing over control of security in the country to Afghans by 2014.