U.S. Marines and Afghan forces killed more than 40 suspected militants in an operation against insurgents who had inflicted the deadliest blow to American forces since the Taliban's ouster, a military spokesman said Monday.

The weeklong operation, which concluded over the weekend, was aimed at rebels in the eastern Koregnal Valley (search) believed responsible for twin attacks that killed 19 troops in June. Three Navy SEALs were killed in an ambush, and all 16 soldiers on a helicopter sent to rescue them died when it was hit by a rocket-propelled grenade.

"It was successful," Lt. Col. Jerry O'Hara told The Associated Press. "We had over 29 separate engagements with enemy forces that resulted in more than 40 enemy killed in action and many others wounded."

O'Hara also announced that a separate three-day battle from Aug. 7-10 in southern Zabul province's Daychopan (search) district left a total of 65 suspected militants dead. The military had previously reported that 16 rebels had been killed.

News of the casualties comes after a deadly period for U.S. forces in Afghanistan, with 13 American troops killed this month. Four soldiers were killed Sunday when a massive bomb exploded under a wooden bridge as a convoy of armored Humvees was crossing it. Three troops were wounded by shrapnel from secondary explosions as they tried to pull the four out of a burning Humvee.

Most of the troops who have been killed were part of an offensive against militants who have vowed to subvert legislative elections on Sept. 18 — the next step toward democracy after more than two decades of war and civil strife.

Some 187 U.S. service members have been killed in and around Afghanistan since the start of Operation Enduring Freedom (search) in late 2001 — including 64 during a rash of insurgent attacks in the last six months, which have left about 1,000 other people dead as well.

The bloodshed has led the military to rush in an airborne infantry battalion of about 700 troops on standby in Fort Bragg, N.C., boosting the number of American troops in Afghanistan to about 20,000. Some 3,100 soldiers from 19 other nations also are members of the U.S.-led coalition.

A separate NATO-led peacekeeping force also has brought in reinforcements ahead of the polls and now numbers about 10,500.

Last Tuesday, a helicopter carrying NATO peacekeepers crashed in a western Afghan desert and another chopper flying with it made an emergency landing, killing 17 Spanish troops and wounding five. Investigators have so far found no evidence that the helicopters were downed by hostile fire.

The Spanish soldiers were training for security operations for the elections, and their deaths marked the NATO force's largest single loss of life in Afghanistan.

The recent violence in Afghanistan pales next to the casualties suffered in Iraq, but it has dampened some of the optimism that prevailed after the country's inaugural presidential election took place took place peacefully last fall and insurgent attacks dropped off during the winter.

In other recent violence, a roadside bomb exploded Sunday near a convoy of U.S. Embassy vehicles on the outskirts of the capital, Kabul, lightly wounding two American staff members, embassy spokesman Lou Fintor said.

In the southern Kandahar province, gunmen riding a motorbike killed senior cleric Mawlawi Abdullah — the latest attack on religious leaders who have openly condemned the Taliban and other extremists.

Two roadside bombs also exploded near police convoys in the southern provinces of Zabul and Uruzgan late Saturday, each killing two officers, officials said.