Story highlights Some U.S. troops killed are thought to be special operations forces, officials say

Besides the 7 Americans, 4 Afghans also died -- 3 soldiers and an interpreter

Other Operation Enduring Freedom copter crashes have killed Americans, Turks this year

In a separate incident, another service member died in southern Afghanistan

Seven American service members were among the 11 people killed in a helicopter crash in southern Afghanistan on Thursday, NATO's International Security Assistance Force said.

Three members of the Afghan National Security Forces and an Afghan civilian interpreter also died in the crash of the UH-60 Black Hawk helicopter. Some of the U.S. troops killed are believed to be special operations forces, according to Pentagon officials.

The cause of the crash is under investigation, ISAF said. Pentagon officials added that investigators will look into the possibility that the aircraft was shot down or suffered a mechanical failure.

The helicopter was on patrol when it went down in the Chinarto area of Shah Wali Kut district in Kandahar province, the Kandahar governor's office said in a statement.

It's not clear whether the helicopter was in the area because of military operations, the office said.

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But military analyst Bill Roggio told CNN he thinks the helicopter could have been involved in a raid, a resupply mission or some sort of special operation because both Afghans and Americans from two different commands were aboard the flight.

Four of the Americans were classified as ISAF service members, and the other three were from United States Forces-Afghanistan.

In a separate incident Thursday, ISAF said another service member died after a bombing in southern Afghanistan. The nationality of the victim was not released.

The violence comes two days after one of the bloodiest days in Afghanistan so far this year, with three separate attacks leaving at least 47 people dead and as many as 145 wounded, according to government and police officials.

Six other helicopter crashes involving Operation Enduring Freedom, the official name for the U.S. operation in Afghanistan, occurred this year, according to a CNN count. Sixteen Americans died in the first five crashes: six in January, four in April and two each in May, June, and July. Four of the crashes occurred in Afghanistan and one was in Oman.

The ones in May and June involved hostilities, and the others have been classified as non-hostile, authorities said.

And in March, 12 Turkish service members died in a helicopter crash in Kabul province.

Last August, 30 Americans and eight Afghans died when the Taliban downed a helicopter near Kabul. Of the 30 killed , 22 were Navy personnel. Seventeen of them were members of the SEALs.

The other eight U.S. troops killed were three Air Force forward air controllers and five Army helicopter crew members.

Roggio -- the managing editor of Long War Journal, a blog that reports and analyzes the war against terror -- said "historically, the number of crashes and shootdowns have been relatively low" during the war.

"They are going to happen. They happen in training," he said.

Current figures are low, he said, compared to the Afghan war against the Soviets in the 1980s when the CIA, he said, supplied and trained jihadis in the use of Stinger missiles, the surface-to-air weapons.

What's different today, Roggio said, is that Taliban militants don't have the same level of equipment, coalition helicopter crews perform better and the aircraft receive excellent maintenance.