Hundreds of Afghan and American soldiers are engaged in a new hunt for Usama bin Laden and other terror suspects in a mountainous region bordering Pakistan, the Afghan military said Monday.

The operation began Friday in Spera, a border district in Khost province (search), 90 miles south of Kabul, Afghan military commander Zakim Khan (search) said. No arrests or clashes were reported.

The 700 troops, including 100 American soldiers backed by U.S. helicopters, blocked off a potential escape route for militants who could be hiding on the Pakistani side of the frontier, Khan said.

"We have reports that this was a route used by both Taliban and Al Qaeda," Khan said. "I don't know how many came and went here, but now they have one option less."

Khan, the commander of the Afghan 822nd border battalion, said that caves in the region were used during the war against Soviet occupation in the 1980s.

"I'm very optimistic we'll find something because the main road is covered with Afghan checkpoints," he said.

The area is across from Pakistan's Waziristan (search) tribal region, long considered a possible hide-out for bin Laden and Al Qaeda No. 2, Ayman al-Zawahri (search).

U.S. military spokesman Lt. Col. Matthew Beevers would not comment on any operations involving the 13,500 U.S.-led coalition in Afghanistan, saying it could jeopardize their success.

American officers have said they are confident that bin Laden, Taliban leader Mullah Omar and rebel Afghan warlord Gulbuddin Hekmatyar (search) will be caught, but last week backed off previous forecasts that it would be this year.

In Pakistan, the government has given tribesmen in the Shawal border area until April 20 to hand over Al Qaeda suspects or face a fierce crackdown.

Senior Pakistani officials initially thought they had al-Zawahri surrounded during a March operation in South Waziristan that saw 160 militants arrested and 63 killed. Some 50 Pakistani troops also died, as well as a dozen civilians.

The U.S. military has said it saw no increase in militants' movements along the border during that operation, but that it expects Pakistan to keep up the pressure.

Beevers said they were ready to execute what commanders have called a "hammer-and-anvil" approach, crushing insurgents with orchestrated operations on both sides of the frontier.

"We're positioned and poised to take care of those guys if they leak across," he said.