Thirty International Security Assistance Force (ISAF) service members, one civilian interpreter and seven Afghan commandos were killed when a coalition CH-47 Chinook helicopter crashed in east Afghanistan on Saturday, said a statement released by NATO on Sunday.

All of the ISAF service members on board were from the U.S. The incident represents the highest number of U.S. forces killed during a single event since the war on terror began in Afghanistan in late 2001, the statement said.

"No words describe the sorrow we feel in the wake of this tragic loss," said U.S. General John R. Allen, the Commander of the NATO-led International Security Assistance Force.

File photo taken on November 20, 2008 shows a Chinook helicopter flying over the mountain areas of Afghanistan's Khost Province. Thirty International Security Assistance Force (ISAF) service members, one civilian interpreter and seven Afghan commandos were killed when a coalition CH-47 Chinook helicopter crashed in east Afghanistan on Saturday. [Xinhua/AFP]

"Our thoughts and prayers are with the families who are now waiting for their loved ones to return home. We will do everything in our power to support them in this time of need."

"We also mourn the loss of our heroic Afghan partners who fight with us shoulder to shoulder, every day," added Allen.

An investigation is underway to determine the exact cause of the crash. Additional details will be provided as they become available.

The incident happened Friday night in Wardak province, according to the statement released by the Afghan presidential office on Saturday. Meanwhile, Shahidullah Shahid, spokesman of the Wardak provincial administration, told Xinhua that a NATO helicopter crashed in Syed Abad district during a military operation Friday night.

Taliban outfit claimed responsibility, saying a helicopter was shot down by militants, according to local media.

The incident came after the U.S. began gradual pullout of 33, 000 combat troops from Afghanistan by the end of summer in 2012.