U.S. President Barack Obama has arrived at Dover Air Force Base to pay his respects to the 30 U.S. troops killed in a helicopter crash in Afghanistan.

The Pentagon says two military planes carrying the remains arrived at the air base in Delaware earlier Tuesday.

Insurgents reportedly shot down the Chinook transport helicopter Saturday, during an anti-Taliban operation in the remote Tangi Valley of Afghanistan's Wardak province. Seven Afghan soldiers and an Afghan interpreter were among the 38 people killed.

The Defense Department says Tuesday's arrival ceremony for the bodies, which include 22 members of the elite Navy SEALS, was closed to the media because the remains are still being identified.

The crash is the worst loss of life suffered by U.S. forces in a single incident from the decade-long war. NATO says an investigation is under way to determine the exact cause of the crash.

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

Pentagon officials said families of the fallen troops were allowed to attend Tuesday's arrival ceremony in Delaware.

President Obama's administration lifted an 18-year ban on media coverage of the return of dead soldiers in 2009, leaving the choice up to relatives of those killed.

U.S. Defense Secretary Leon Panetta said Monday that as heavy a loss as the crash 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 apparent downing of the helicopter by a Taliban rocket-propelled grenade was a single combat incident and did not represent any watershed or trend in the war against the Taliban.

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.