Three rockets landed near a U.S. base in eastern Afghanistan on Monday but — as in a similar attack just days ago — exploded without causing casualties.

In the southeast and east, coalition troops sweeping Afghan highlands for Al Qaeda and Taliban destroyed cave hide-outs and sighted camouflaged buildings, military spokesmen said.

The rockets exploded at 2 a.m. several hundred yards from U.S. soldiers in the eastern town of Khost, spokesman Maj. Bryan Hilferty said.

A small team of U.S. special operations forces is based in Khost, where fighting between rival police commanders two weeks ago killed several people.

On Thursday, U.S. officials said three mortar rounds or rockets exploded several hundred yards from the airfield in Khost. As on Monday, no injuries were reported and it was unclear who fired the projectiles.

"They're generally set up the same way," Hilferty said. "They put them on a little tripod, you just build two sticks together, and you put a rocket on there and you put on a timer, and the rocket goes off when the timer goes off."

Hilferty said coalition and Afghan military forces seized a large cache of rocket, mortar and machine-gun ammunition near the spot where the rockets were launched Monday.

Elsewhere, the search for Al Qaeda or Taliban continued on several fronts.

Canadian Lt. Luc Charron said a separate, Canadian-led operation in eastern Afghanistan was going "extremely well."

He said military engineers were destroying caves and complexes after searching for anything of potential intelligence value. Charron said the caves were being destroyed to prevent al-Qaida fighters from using them.

In the southeast, Royal Marines spokesman Lt. Col. Paul Harradine said British-led troops had nearly finished the first phase of Operation Snipe, reaching the top of two craggy mountains more than 11,000 feet high.

The 1,000-man British-led operation is aimed at sweeping through a previously unexplored area in search of Taliban or al-Qaida guerrillas.

"They have now almost finished the first phase of the operation which is clearing the highest part of the area they're in," Harradine said. Over the next 24 hours, they will begin moving into position to sweep the valleys below, he said.

Harradine said troops scanning the far side of a valley had seen an "uninhabited and very well camouflaged newly built settlement" they would soon move through. He said it consisted of a few mud buildings and outhouses and was covered with shrubs, bushes and trees.

Officials in Afghanistan won't give the location of the operation. But military officials in Washington said week it was southeast of Operation Anaconda, the U.S.-led ground assault in March in the Shah-e-Kot area near the Pakistani border.

The Canadian-led and British-led missions are part of Operation Mountain Lion, the U.S.-led search for Taliban and Al Qaeda holdouts in eastern Afghanistan. Both missions are backed by Afghan forces, U.S. special operations troops and U.S. air support.

No enemy contact has been reported.

Many fugitives are thought to have fled east into Pakistan's rugged tribal region. In an effort to seal off that escape route, a top Pakistani security team left Monday for Washington to seek help in tightening control over the porous 870-mile border with Afghanistan.

In northern Afghanistan, a spokesman for Gen. Abdul Rashid Dostum said up to 400 Pakistanis who fought for the Taliban will soon be freed from Shibergan prison. Faizullah Zaki said there are 1,500 Afghans and 800 Pakistanis in the prison.