KABUL, Afghanistan – U.S. and Afghan troops killed at least 40 suspected rebels in an offensive, targeting militants who ambushed Navy SEAL commandos and shot down a special-forces helicopter – the deadliest attacks on U.S. forces in Afghanistan, U.S. officials said Monday.

The military declared the weeklong operation in lawless Kunar province near Pakistan a success, following the spate of insurgent attacks that already has made 2005 the bloodiest year for American forces in the country since the Taliban’s ouster.

This year alone, 66 American service members have been killed – more than a third of the 187 who have died in and around Afghanistan since 2001. Four were slain Sunday when a massive roadside bomb blew up an under armored Humvee.

The offensive, centered on eastern Kunar province’s Korengal Valley, sought rebels suspected of killing three Navy SEAL commandos in an ambush and 16 troops aboard a special-forces helicopter that was shot down June 28. The operation ended over the weekend.

“It was successful,” spokesman Lt. Col. Jerry O’Hara told the Associated Press. “We had over 29 separate engagements with enemy forces that resulted in over 40 enemy killed in action and many others wounded.”

Before the operation started, hundreds of Afghan rebels, as well as militants from Pakistan, Saudi Arabia and Chechnya, were believed to be hiding in the valley, just miles from the Pakistan border, and gearing up for attacks on polling stations.