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 U.S. military is paying in the decade-long Afghan war.

A military helicopter was shot down in eastern Afghanistan, killing 30 U.S. special operation troops, most of them from the elite Navy SEALs unit that killed al-Qaida leader Osama bin Laden, along with seven Afghan commandos. It was the deadliest single incident for American forces in the decade-long war.

U.S. officials believe that none of those who died in the crash had participated in the bin Laden raid, although they were from the same unit that carried out that mission, two officials told The Associated Press. They spoke about matters of military security on condition of anonymity.

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. The White House had no comment about the details of who died or what happened.

"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."

National security adviser Tom Donilon first notified Obama of the incident shortly after 8 p.m. EDT Friday. The president spoke again to Donilon later Friday night and received a paper briefing both that evening and Saturday morning.

Obama issued his written statement just shy of 10 a.m. Saturday. A half-hour later, Obama, at Camp David, was briefed via conference call by Defense Secretary Leon Panetta, White House chief of staff Bill Daley, Joint Chiefs of Staff Chairman Adm. Mike Mullen, Donilon and members of the president's national security staff.

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

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.

Panetta said he was saddened by the deaths of the Americans and Afghans.

"Their courage was exemplary, as was their determination to make this a safer world for their countries and for their fellow citizens," Panetta said in a statement. "We will stay the course to complete that mission, for which they and all who have served and lost their lives in Afghanistan have made the ultimate sacrifice. They and their families are in my thoughts, in my prayers and in my heart."

Mullen warned against jumping to conclusions about the incident before investigators have completed their work. He also asked that the process of informing family members be respected, no matter how long it takes, and that people remember that "the troops we lose in this war aren't just statistics or numbers on a wall."

"They were parents and siblings, and someone's child. We need to make sure we do all we can to comfort and support the families whose lives are now forever changed," he said in a statement.

Mullen also said Americans must remain committed to the mission.

"The fight goes on. These brave Americans volunteered to serve their country," he said. "They risked their lives doing it. They gave their lives doing it. The best way we can honor that sacrifice is to keep at it, keep fighting, keep moving forward. I'm certain that is what our fallen would have wanted, and it is certainly what we are going to do."

The toll Saturday surpassed the worst single-day loss of life for the U.S.-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.