A U.S. military helicopter crashed early Saturday in eastern Afghanistan, killing 30 Americans in the deadliest incident for U.S. troops since the war began. Seven Afghan commandos were also killed.

Sources told NPR the Taliban shot down the helicopter as it was on a special overnight mission targeting an insurgent compound in Wardak province.

Many of those killed were Navy SEALs, but sources said they were not the ones involved in the May raid that killed al-Qaida leader Osama bin Laden.

“Their deaths are a reminder of the extraordinary sacrifices made by the men and women of our military and their families, including all who have served in Afghanistan,” President Obama said in a statement, adding that his thoughts and prayers go out to the families of those who died.

The U.S.-led coalition said that 30 American service members, a civilian interpreter and seven Afghan commandos were killed when the CH-47 Chinook crashed in the early hours Saturday. A current U.S. official and a former U.S. official said the Americans included 22 SEALs, three Air Force air controllers, and a dog handler and his dog. The two spoke on condition of anonymity because military officials were still notifying the families of the dead.

Afghan President Hamid Karzai, the first public figure to announce the number of people killed in the crash and the presence of special operations troops, offered his condolences to the families of those killed.

The deaths bring to 365 the number of coalition troops killed this year in Afghanistan and 42 this month.

“No words describe the sorrow we feel in the wake of this tragic loss,” Marine Corps Lt. Gen. John Allen, the top general in Afghanistan, said. “All of those killed in this operation were true heroes who had already given so much in the defense of freedom.”

The overnight raid took place in the Tangi Joy Zarin area of Wardak’s Sayd Abad district, about 60 miles southwest of Kabul. Forested peaks in the region give the insurgency good cover and the Taliban have continued to use it as a base despite repeated NATO assaults.

“Eastern Afghanistan is increasingly becoming the big fight in Afghanistan now that the southern part of the country — Kandahar and Helmand provinces — are becoming more pacified,” NPR Pentagon correspondent Tom Bowman said on All Things Considered.

Taliban spokesman Zabiullah Mujahid said in a statement that the helicopter was involved in an assault on a house where insurgent fighters were gathering. During the battle, the fighters shot down the helicopter with a rocket, he said.

An American official in Brussels said the helicopter was a twin-rotor Chinook, a large troop and cargo transporter. Bowman said Chinooks are often used in special operations missions because they can carry a lot of people and equipment.

“In Afghanistan, they really rely a lot on helicopters because the road structure is so primitive — many dirt roads and gravel roads, very few paved roads,” Bowman said. “If you want to get anywhere fast, you’re taking a helicopter.”

The casualties are believed to be largest loss of life in the history of SEAL Team Six, officially called the Navy Special Warfare Development Group, or DEVGRU. The team is considered the best of the best among the already elite SEALs, which numbers 3,000 personnel.

The death toll surpasses the previous worst single day loss of life for the U.S.-led coalition in Afghanistan since the war began in 2001 — the June 28, 2005, downing of a military helicopter in eastern Kunar province.

In that incident, 16 Navy SEALs and Army special operations troops were killed when their craft was shot down while on a mission to rescue four SEALs under attack by the Taliban. Three of the SEALs being rescued were also killed and the fourth wounded.

Afghanistan has more U.S. special operations troops, about 10,000, than any other theater of war. The forces, often joined by Afghan troops, carry out as many as a dozen raids a night and have become one of the most effective weapons in the coalition’s arsenal, also conducting surveillance and infiltration.

“But these missions are also very controversial,” Bowman said. “President Karzai has condemned them because sometimes civilians get caught in the crossfire or they go to the wrong house.”

NATO commanders have said the raids are safer for civilians than relatively imprecise airstrikes.

From April to July this year, special operations raids captured 2,941 insurgents and killed 834, twice as many as those killed or captured in the same three-month period of 2010, according to NATO.

The coalition plans to increase its reliance on special operations missions as it reduces the overall number of combat troops.

The site of the crash, Tangi, is a particularly dangerous area, the site where many of the attacks that take place in the province are planned, said Wardak’s Deputy Gov. Ali Ahmad Khashai. “Even with all of the operations conducted there, the opposition is still active.”

The U.S. Army had intended to hand over its Combat Outpost Tangi to Afghan National Security Forces in April, but the Afghans never established a permanent base there. “We deemed it not to be stategic and closed it,” said coalition spokesman U.S. Army Maj. Jason Waggoner. “The Taliban went in and occupied it because it was vacant.”

Western military commanders have been debating moving forces from other areas in Afghanistan to reinforce troops around the capital and in the east, where the Taliban is often aided by al-Qaida and other terrorist groups. Earlier this year, the U.S. military closed smaller outposts in at least two eastern provinces and consolidated its troops onto larger bases because of increased insurgent attacks and infiltration from the Pakistan border.There have been at least 17 coalition and Afghan aircraft crashes in Afghanistan this year.

Most of the crashes were attributed to pilot errors, weather conditions or mechanical failures. However, the coalition has confirmed that at least one CH-47F Chinook helicopter was hit by a rocket propelled grenade on July 25. Two coalition crew members were injured in that attack.

Material from The Associated Press was used in this report.

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