A roadside bomb killed four U.S. soldiers and wounded three Sunday as they were patrolling in southern Afghanistan (search), the deadliest attack on American forces here in nearly two months, the U.S. military said.

Also Sunday, a roadside bomb exploded near a convoy of U.S. Embassy vehicles, wounding two American officials, an embassy spokesman said. Police officials said the blast occurred on the western outskirts of Kabul (search).

Militant assaults elsewhere killed a senior pro-government Islamic leader and two Afghan policemen, as Taliban-led rebels step up a campaign to subvert key Sept. 18 legislative elections. Seven U.S. soldiers have been killed in Afghanistan over the past four days.

Sunday's blast that killed U.S. troops occurred in Zabul (search) province's Daychopan district, the military said in a statement. The three wounded soldiers were hit by shrapnel and were in stable condition, the military said.

"The unit was conducting offensive operations in support of an ongoing mission to find and defeat enemy forces in the area when the attack occurred," the statement said. "The unit's mission is part of a much larger operation to disrupt enemy forces and to thereby provide a safe environment for upcoming September elections."

The statement quoted Maj. Gen. Jason Kamiya, the U.S.-led coalition's operational commander, as saying the attack would "strengthen, not weaken, the resolve" of the force.

Some 187 U.S. service members have been killed in and around Afghanistan since the start of Operation Enduring Freedom in late 2001 — including 64 during an upsurge of insurgent attacks in the last six months that have also left about 1,000 others dead.

On Friday, a U.S. Marine was killed in a clash near Asadabad in eastern Afghanistan, while a day earlier, a roadside bomb killed two U.S. soldiers as they were protecting road workers on a U.S.-funded project in southern Kandahar province, a former Taliban stronghold.

U.S. officials have warned that fighting could escalate ahead of the parliamentary and provincial assembly elections, seen as the next step in building Afghanistan's democracy after a quarter-century of civil strife and war.

In attacks elsewhere, a roadside bomb exploded late Saturday under a police vehicle also in Zabul province, killing two police officers, said local government chief Rozi Khan.

In southern Kandahar province Sunday, gunmen riding a motorbike shot dead cleric Mawlawi Abdullah, the latest in a string of attacks on religious leaders who have openly condemned the Taliban and other extremists.

Abdullah — a senior figure in the Islamic Ulama Council — and a colleague were killed as they walked out of a mosque after praying at dawn, Interior Ministry official Dad Mohammed Rasa said.

In the eastern province of Kunar, rebels ambushed two tanker trucks hauling fuel to an American military base, burning the vehicles but letting the drivers go, officials said.