Karikot, Pakistan ? Pakistani attack helicopters and artillery today pounded hundreds of al-Qaida suspects and tribesmen hunkered down in mud fortresses in a border region, where al-Qaida No. 2 Ayman al-Zawahri is believed hiding.

Up to 400 militants are believed holed up in the heavily fortified compounds in South Waziristan — a forbidding tribal region near Afghanistan.

“The operation is on,” army spokesman Maj. Gen. Shaukat Sultan said today.

He reported no arrests of any senior al-Qaida member.

An Associated Press reporter in Wana, the main town of South Waziristan, said a helicopter gunship pounded Gangikhel village on the western outskirts of Wana this morning, an indication that the operation may be expanding.

The village had not been targeted since the new offensive was launched Tuesday.

Fighting stopped in the evening on Friday, but late into the night the troops began firing artillery guns, an intelligence official in Wana said on the condition of anonymity.

On Friday, Sultan said the Pakistani forces were joined by “a dozen or so” American intelligence agents in the ongoing operation.

U.S. satellites, Predator drones and other surveillance equipment hovered overhead.

Authorities hoped to wrap up the raid by Sunday afternoon, Interior Minister Faisal Saleh Hayyat told The Associated Press. Dozens have been killed in the four-day operation.

Across the Afghan border a few miles away, U.S. and Afghan forces tightened a net along the rugged frontier and reported arresting midlevel terrorist leaders in recent days.

Soldiers of Pakistan's paramilitary force take positions outside Wana, capital of a Pakistani tribal area in South Waziristan where a battle is going on between the Pakistan army and fugitive al-Qaida terrorists. The Pakistani army used heavy artillery and helicopters Friday to take aim at terrorists hiding along the Pakistan-Afghanistan border.