BAGRAM AIR BASE, Afghanistan — The nine NATO coalition members who died in a helicopter crash in southern Afghanistan early Tuesday included five U.S. soldiers attached to the 101st Airborne Division and at least some American special operations troops, according to two U.S. military officials.

The data recorder from the helicopter has been recovered, one official said.

The crash occurred in Zabol province, a Taliban stronghold near Kandahar province and the Pakistani border. Kandahar is the focus of a large offensive by U.S. forces that has been described as pivotal by senior commanders.

The Pentagon has not released the names of the victims, though it is expected to do so soon. A memorial service for some of the Americans is to be held at a base near Kandahar on Friday, the officials said.

The U.S. officials spoke on condition of anonymity because details of the crash had not been released by the Pentagon. The withholding of such information more than 48 hours after an event is unusual; normally the nationalities and sometimes the branch of service of slain NATO troops are disclosed by the following day.

An Afghan soldier and an American civilian were injured in the crash, the International Security Assistance Force said in a statement Tuesday.

The cause of the crash has not been disclosed, but coalition officials said at the time that there were no reports of enemy fire in the area. The Taliban said its fighters had shot down the craft, but such claims are often false.

Taliban fighters have not shot down Western helicopters in large numbers, though they did hit a Canadian chopper last month in Kandahar province, injuring eight troops. Another helicopter was shot down in June in Helmand province, killing four Western troops.

U.S. special operations troops have stepped up operations in southern Afghanistan in recent months and often travel the rugged region at night by helicopter. North Atlantic Treaty Organization officials have said such raids have resulted in the arrests or deaths of thousands of mid-level Taliban figures.

Elsewhere in Afghanistan, NATO said militants attacked an outpost held by coalition and Afghan troops in Khowst province. At least 25 insurgents were killed, military officials said Wednesday.

Gen. Raz Mohmmad Horya Khil, a senior commander of the Afghan National Army in the province, said the assailants attacked the Mir Safar outpost from the Pakistani side of the border late Tuesday in a battle that lasted for more than two hours, according to the Associated Press. Helicopters were called in to provide support.

In Copenhagen, meanwhile, military authorities said a bomb in southern Afghanistan killed a Danish soldier and seriously injured another, the Associated Press reported. At least 36 Danes have been killed serving in Afghanistan, according to the independent website icasualties.org.

With support for the war wavering among NATO allies, combat casualties in nations with relatively small contingents in Afghanistan have powerful reverberations at home.

This has been the deadliest year for NATO forces in the nine-year war. With Tuesday’s crash, 529 members of the international force have been killed in 2010, according to icasualties.org. The previous high was 2009, when 521 Western troops were killed. Combat deaths in June and July rose to the highest levels of the conflict.