The government ordered a halt to the operation to allow some of the 300,000 families who fled air strikes and combat in the Bajur region to return home for the Muslim holy month of Ramadan.

However, officials reported that troops fired on militants seen moving toward a security post late yesterday, and that stray mortar shells killed at least two civilians.

U.S. officials recently stepped up calls for Pakistan to put more pressure on militants using bases in its remote tribal areas to mount cross-border attacks also on NATO and government troops in Afghanistan.

Some analysts have warned that the pause in the weeks-long Bajur operation would only allow the militants to regroup.

Pakistani officials said yesterday, however, that their forces had killed at least 560 Pakistani and foreign fighters and thwarted a push to make Bajur a militant fortress.

Maj. Gen. Athar Abbas, an army spokesman, said about 20 members of the security forces died and 30 were missing.

"In our view, the back has been broken," Abbas told the Associated Press. "Main leaders are on the run, and the people of the area are now openly defying whatever the militants had achieved there."

Officials including former Pakistani President Pervez Musharraf have mentioned Bajur as a possible hiding place for bin Laden or Zawahiri.

Abbas said that many foreigners were reportedly in Bajur before the operation, but that many had probably fled to Afghanistan or other parts of Pakistan's northwest and that the operation had turned up no trace of the al-Qaeda chiefs.

Interior Ministry chief Rehman Malik said yesterday that authorities also received a report that Zawahiri's wife had been in the neighboring tribal region of Mohmand.

Pakistani forces stormed the location but didn't find the couple, he said, without indicating when the raid took place. He said Zawahiri moved between Mohmand and the Afghan provinces of Kunar and Paktika.