A NATO helicopter crashed in Afghanistan's east on Monday but there were no apparent casualties, officials said, another stark reminder of the dangers of the war after 38 people were killed in an air incident, the largest single loss for foreign forces in 10 years.

A worrying surge of military deaths is being matched by record casualties among civilians, who continue to bear the brunt of a war that appears to have become bogged down despite claims of success from both sides.

On Monday, three hundred angry Afghans took to the streets in central Ghazni province carrying the bodies of two people they claimed had been killed during a raid by ISAF troops.

Civilian casualties caused by foreign troops hunting insurgents have long been a major source of friction between Kabul and its Western backers. U.N. figures show such casualties hit record levels in the first six months of 2011, although it blamed 80 percent of them on insurgents.

NATO officials are still investigating the cause of a helicopter crash two days ago that killed 38 people, including 30 U.S. soldiers -- some from the Navy's special Forces SEAL Team 6 that killed Osama bin Laden -- seven Afghans and an interpreter.

The Taliban claim to have shot down that troop-carrying CH-47 Chinook helicopter in central Maidan Wardak province and a U.S. official in Washington, who asked not to be identified, said that helicopter was believed to have been shot down.

"We're still not aware of the cause of the incident, this is a very vital part of the investigation," Brigadier General Carsten Jacobsen, senior spokesman of the NATO-led International Security Assistance Force (ISAF), told a news conference.

"The area in which the helicopter was operating was known to be not free of insurgents."

Separately, another ISAF helicopter had made a "hard landing" in Paktia province, a volatile area in Afghanistan's southeast, another official said.

"There were no casualties," another ISAF spokesman Lieutenant Colonel David Doherty said. An investigation was underway but it appeared there was no enemy activity in the area at the time.

Taliban spokesman Zabihullah Mujahid claimed in a text message sent to Reuters that the Islamist group had shot down the helicopter, another Chinook, in the Zurmat district of Paktia, killing 33 American soldiers.

The Taliban often exaggerate claims in attacks against foreign troops and Afghan security forces and government targets, although they correctly identified the number killed in the weekend's Chinook crash in Wardak.

DEVASTATING TOLL

At least another seven ISAF troops were killed in fighting in a ghastly 48 hours for the coalition. Four were killed in two separate attacks on Sunday, including two French legionnaires.

The spike in casualties -- at least 383 foreign troops have been killed so far this year, almost 50 of them in the first week of August -- comes at a time of growing unease about the increasingly unpopular and costly war.

U.S. and NATO officials issued statements vowing to "stay the course" in Afghanistan after the deadly weekend Chinook crash but the recent devastating death toll will likely raise more questions about how much longer foreign troops should stay in Afghanistan.

The deaths came barely two weeks after foreign troops began the first phase of a gradual process to hand security responsibility over to Afghan soldiers and police.

That process is due to end with the last foreign combat troops leaving at the end of 2014, but some U.S. lawmakers are already questioning whether that timetable is fast enough.

Afghan President Hamid Karzai issued a statement on Sunday saying "enemies of Afghanistan" -- the Taliban and other insurgents -- wanted to disrupt the transition process.

In Ghazni, deputy police chief Mohammad Hussain said almost 300 people had gathered to carry two bodies to the provincial governor's office after an overnight raid by ISAF in the Khogyani district.

"People claim the corpses are from civilians killed during a night raid by ISAF forces, but still they are not identified," Hussain told Reuters.

ISAF spokesman Captain Pietro D'Angelo said two insurgents had been killed after a patrol came under attack.

"There are no reports of civilians harmed during this operation," D'Angelo said.

ON Sunday, Karzai ordered an investigation into a NATO air strike that allegedly killed eight civilians in volatile southern Helmand province on Friday.

U.N. figures show that 1,462 Afghan civilians were killed in conflict-related incidents in the first six months of 2011, the deadliest period for civilians since the Taliban were toppled by U.S.-backed Afghan forces in late 2001.

Foreign military deaths also hit record levels in 2010 with 711 killed, with 2011 following a similarly bloody trend.