DERA ISMAIL KHAN, Pakistan - Two top al Qaeda operatives were among four foreign militants killed in a suspected U.S. missile strike in Pakistan's volatile northwest, Pakistani intelligence officials said Wednesday.

The officials said one was in charge of the terror network's activities in Pakistan's tribal regions, semi-autonomous areas that the U.S. fears have become a haven for al Qaeda and Taliban fighters involved in attacks on American and NATO forces in neighboring Afghanistan.

The suspected missile strike occurred Monday in North Waziristan, destroying a seminary and houses associated with a Taliban commander. It was one of a series of such strikes in recent days in Pakistan, indicating the U.S. may be escalating its efforts to crack down on militants along the lengthy, porous Afghan-Pakistan border.

Three Pakistani intelligence officials identified four foreign militants killed in the strike as Abu Qasim, Abu Musa, Abu Hamza and Abu Haris. The officials spoke on condition of anonymity because of the sensitivity of their jobs.

Abu Haris led al Qaeda efforts in the tribal areas, while Abu Hamza led activities in Peshawar, the main northwest city, said the intelligence officials, who said they got the details from informants and agents in the field.

Abu Haris' nationality had yet to be confirmed, but Abu Hamza was from Saudi Arabia, the officials said. Abu Hamza was believed to be a bomb-making expert as well. Abu Qasim was Egyptian, while Abu Musa also was Saudi, but both appeared to be lower-ranking al Qaeda members, the officials said.

An army spokesman, Maj. Murad Khan, said Wednesday the military had no information about the identity or nationality of the men killed in what he called "explosions" in North Waziristan.

"We don't know who died in the explosions there," he said.

Two of the intelligence officials said Tuesday that the overall death toll from the strike rose to 20 after residents and militants pulled more bodies from the rubble.

The targets were associated with Jalaluddin Haqqani, a veteran of the fight against Soviet troops in Afghanistan in the 1980s who American commanders now count as a dangerous foe.

Haqqani and his son, Siraj, have been linked to attacks this year including an attempt to kill Afghan President Hamid Karzai and a suicide attack on a hotel in Kabul. Haqqani network operatives plague U.S. forces in Afghanistan's eastern Khost province with ambushes and roadside bombs.