The U.S. military has launched a new operation in Afghanistan (search) involving thousands of troops to protect the upcoming presidential election, the top American commander said Tuesday.

The operation, named Lightning Resolve, is "kicking off as we speak," Lt. Gen. David Barno told The Associated Press in an interview at his headquarters in the Afghan capital.

He said the operation contains enough "offensive punch" to keep militants off-balance and would include targeted, intelligence-driven raids. He gave no specifics.

A 2,000-strong Marine force which has hammered Taliban (search) militants in a southern stronghold since it arrived in March is in the process of leaving the country, Barno said.

The remaining force of 17,000 soldiers will intensify its cooperation with the United Nations (search), which is helping organize the Oct. 7 presidential election, seen as a key step on this war-shattered country's path to recovery.

The U.N. has helped register some 7 million voters, despite a string of attacks that has raised fears that security will not be adequate to ensure a fair and free vote.

"We'll be shifting our efforts to helping to build the required security going into the election itself," Barno said. "The specifics of that plan are still being worked out."

U.S. forces are expected to provide broad security across the south and east during the election, leaving Afghan police and soldiers to protect polling stations.

NATO (search) is expected to increase its 6,500-strong peacekeeping force focused on Kabul and fan out across the relatively peaceful north in the run-up to the vote.

Peaceful elections would reflect well on the U.S. military and deflect criticism that it has failed to capture Usama bin Laden (search) or Taliban supreme leader Mullah Mohammed Omar. The military is also dealing with a widening investigation into allegations that Afghan prisoners have been abused in American jails here.

Barno said the effort to track down top fugitives was "as robust as it's ever been here." But he said he still he had no firm intelligence on their whereabouts.

There have been reports from Washington that bin Laden and his top aide, Ayman al-Zawahri, might be planning major new Al Qaeda (search) attacks to disrupt the upcoming U.S. elections. But Barno said he had no knowledge of the men's whereabouts or activities.

"Those are, I think, the most difficult targets we have over here," Barno said. "Because of the lack of information we have on them, I think the inference is that they are well-protected."

He said U.S. intelligence-gatherers were hoping that Pakistani military operations against Al Qaeda suspects in a tribal region across the border would produce vital leads.