Washington: As the US mourned the death of its 30 soldiers, including Navy SEALs from the broader unit that killed Osama bin Laden, in a chopper crash in Afghanistan, a probe has been launched to determine the exact cause of the incident that led to the biggest single loss for American troops in the decade-long war.

"No words describe the sorrow we feel in the wake of this tragic loss" of 38 lives -- 30 US troops, seven Afghan commandos and an interpreter, General John R Allen, International Security Assistant Force Commander (ISAF), said in a statement from Kabul.

Following the crash on Saturday, the Afghan Taliban claimed that its militants shot down the helicopter in Wardak province of Afghanistan, according to SITE intelligence.

Among those killed in the deadliest attack on the foreign troops were 25 US special operations forces troops, including 22 Navy SEALS from the same group which was involved in the covert US military operation to kill al-Qaeda leader Osama bin Laden in May this year. But none of the SEAL members, who died on Saturday, were personally involved in the Osama operation.

Besides, five more US soldiers, seven Afghan troops and an interpreter died in the crash of the helicopter during an anti-Taliban operation.

"All of those killed in this operation were true heroes who had already given so much in the defence of freedom," Allen said.

An investigation is underway to determine the exact cause of the crash, the ISAF statement said.

"This tragic incident, once again reminds us of the tremendous sacrifices the brave soldiers of our two countries are making every day alongside each other to bring peace and security to our nations and to make the world a safer place for all of us," Afghan Ambassador to the US, Eklil Hakimi, said.

Senate Majority Leader, Harry Reid, said: "Their sacrifice will not be in vain. Every single day, our men and women in uniform put their lives at risk to defend our nation and make the world a safer place."

The tragedy "is a sobering reminder of their selfless commitment to our nation," he said.

"This tragedy is felt by all Americans, and especially by our men and women in uniform, who continue to do more than their fair share to keep America safe," said Senator John McCain.

Senator Joe Lieberman mourned the loss of "the brave heroes in Afghanistan who have paid the ultimate sacrifice so that we may be safe and free."

"The American patriots who we lost today were among the very best of our best, and they were fighting in a just and necessary war. They served with extraordinary courage and talent, dedicating their lives to our nation."