WASHINGTON: President Barack Obama said Saturday that the deaths of Americans in a helicopter crash in Afghanistan are a reminder of the ''extraordinary'' price the US military is paying in the decade-long Afghan war.

Obama's statement did not confirm the number killed or other details of the crash.

Afghan President Hamid Karzai said that the crash killed 31 US special operation troops and seven Afghan commandos.

But The Associated Press has learned that more than 20 Navy SEALs were among those lost in the crash.

None of those killed in the crash is believed to have been part of the SEALs mission that killed wanted terrorist Osama bin Laden mission, but they were from the same unit as the bin Laden team.

The troops from SEAL Team Six were flown by a US Army crew, according to AP military sources.

One source says the team was thought to include 22 SEALs, three Air Force air controllers, seven Afghan Army troops, a dog and his handler, and a civilian interpreter, plus the helicopter crew.

Earlier, a senior administration official said the helicopter that crashed in eastern Afghanistan was apparently shot down by insurgents in the deadliest single incident of the conflict for US forces. The official spoke on condition of anonymity because the crash is still being investigated.

Obama, who learned of the incident at Camp David, issued a statement saying his thoughts and prayers go out to the families of those who perished.

''Their deaths are a reminder of the extraordinary sacrifices made by the men and women of our military and their families, including all who have served in Afghanistan,'' the president said.

''We will draw inspiration from their lives, and continue the work of securing our country and standing up for the values that they embodied.''

Obama said he also mourned the loss of seven Afghans ''who died alongside our troops in pursuit of a more peaceful and hopeful future for their country.''

Karzai sent his condolences to Obama, according to a statement issued by his office.

At the Pentagon, Defense Secretary Leon Panetta says he is deeply saddened by the loss, and vowed that the US will stay the course to complete the mission to make the world a safer place.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, says the best way to honor their sacrifice is to keep fighting. He asks for patience as the military works to notify families of their losses.

The Taliban claimed to have brought the helicopter down with a rocket attack, but similar claims in the past have proven to be exaggerated.

Nato officials in Afghanistan said they were trying to determine the details of what happened, but they acknowledged there was ''enemy activity'' in the area.

The toll Saturday surpassed the worst single-day loss of life for the US-led coalition in Afghanistan since the war began in 2001 _ the June 28, 2005 downing of a military helicopter in eastern Kunar province.

In that incident, 16 Navy SEALs and Army special operations troops were killed when their craft was shot down while they were attempting to rescue four SEALs under attack by the Taliban.