NATO is probing the cause of a helicopter crash in the central Afghan province of Wardak, where 38 coalition members, including 22 personnel from the elite U.S. Navy SEALS, were killed when their aircraft went down early Saturday.

NATO spokesman, Brigadier General Carsten Jacobsen, said Monday the crash site has been secured and nobody is allowed into the area while the probe is ongoing.

The Chinook transport helicopter went down during an anti-Taliban operation in the remote Tangi Valley. Thirty U.S. troops, seven Afghan commandos and an Afghan interpreter died in the incident — the worst loss of life suffered by U.S. forces in a single incident from the decade-long war.

In Washington Monday, President Barack Obama said the loss of the 30 American troops is “a stark reminder” of the risks that U.S. forces take every day.

U.S. Defense Secretary Leon Panetta said that as heavy a loss as this was, it would be even more tragic if it were allowed to derail efforts to defeat al-Qaida and deny the terrorist group a safe haven in Afghanistan.

Pentagon spokesman Colonel Dave Lapan said the downing of the helicopter was a single combat incident and did not represent any watershed or trend in the war against the Taliban.

Also Monday, Pentagon officials announced that the remains of U.S. soldiers killed in the crash were on their way to Dover Air Force Base. They stressed, however, that news media will not be able to cover the ceremony for the arrival of the fallen troops because the remains are still being identified.

Earlier Monday, another coalition helicopter made a hard landing in the eastern Afghan province of Paktia. NATO said there were no casualties and that there were no initial reports of enemy activity in the area. An investigation into the cause of the incident is under way.

Violence in Afghanistan is at its worst since the U.S.-led invasion in late 2001, with international troop and Afghan civilian deaths reaching record levels.