Kabul, Afghanistan ? Thousands of American troops have begun a new operation to prevent militants from derailing Afghanistan’s first presidential election, the top U.S. commander here said Tuesday in an interview with The Associated Press.

Lt. Gen. David Barno insisted the switch did not blur the military’s focus on catching Osama bin Laden and other top fugitives. But he acknowledged he had no firm idea where the al-Qaida leader was hiding or what he might be planning.

Operation Lightning Resolve is “kicking off as we speak,” Barno said at his headquarters in the Afghan capital.

He said the operation contained enough “offensive punch” to keep militants off balance and could see an increase in targeted, intelligence-driven raids. He gave no specifics.

A 2,000-member Marine force, which has hammered Taliban 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 regular and special operations soldiers will try to fill the vacuum while intensifying its cooperation with the United Nations.

The world body has registered more than 7 million voters for the Oct. 9 election, seen by many war-weary Afghans as well as the United States as vital to Afghanistan’s recovery.

Six election workers are among about 600 people killed in violence this year, victims of feuding warlords, as well as rebels and soldiers — a mix that raises fears the vote will be neither fair nor free.

Barno said the Marines, who have killed scores of suspected militants in intensive operations since May, have helped registration to be a success.

An Afghan woman gets her voter identity card as other women wait at a voter registration center in one of the mosques in Kabul, Afghanistan. American commander in Afghanistan Lt. Gen. David Barno said the U.S. military was launching a new operation named Lightning Resolve, involving thousands of troops, to protect Afghanistan's Oct. 9 presidential election from interruption by militants.

“Now we’ll be shifting our efforts to helping to build the required security going into the election itself,” Barno said. “We should expect that we have to fight to get to these elections.”

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

NATO also has begun topping up its 6,500-strong peacekeeping force focused on Kabul.