The United States government has said it will stay the course in Afghanistan.
Yesterday, it was confirmed that a US helicopter - shot down in eastern Afghanistan - was carrying special forces from the Navy Seals unit that killed Osama Bin Laden in May.
30 US servicemen, seven Afghan commandos and a civilian interpreter were on the aircraft.
The Taliban quickly claimed to have shot down the helicopter with a rocket-propelled grenade.
The Pentagon and the NATO-led International Security Assistance Force (ISAF) in Afghanistan said overnight the cause of the crash was being investigated.
The crash and its high death toll occurred two weeks after foreign forces started a security handover to Afghan troops and police - to be completed by the end of 2014 - and at a time of growing unease about the increasingly unpopular and costly war.
The Chinook crashed in central Maidan Wardak province, just west of the country's capital, Kabul, on Friday night.
'No words describe the sorrow we feel in the wake of this tragic loss,' General John Allen, who took over from General David Petraeus three weeks ago as ISAF commander, said in a statement.
'All of those killed in this operation were true heroes who had already given so much in the defence of freedom.'
A US official said some of the dead Americans were members of the Navy's special forces SEAL Team 6 - the unit that killed al-Qaeda leader Osama bin Laden in May in Pakistan - but that none of the dead had been part of the Bin Laden raid.
The crash was the deadliest single incident for US troops in Afghanistan, ISAF said.
Afghan President Hamid Karzai 'shared his deep sorrow and sadness' with his US counterpart, Barack Obama, and the families of the victims.
Last year was the deadliest of the war for foreign troops in Afghanistan with 711 killed.
The crash in Maidan Wardak means at least 375 foreign troops have been killed so far in 2011.
More than two-thirds were American, according to independent monitor www.icasualties.com and figures kept by Reuters.
