BAGHDAD - Nearly 1,000 people have been detained in a sweep to break al-Qaeda in Iraq's sway in Iraq's third-largest city, Mosul, but many of the fighters have fled to nearby areas, where troops are hunting for them, Iraqi officials said yesterday.

Iraq's leaders presented the crackdown as a success so far in depriving the terrorist network of what has been its most prominent urban stronghold since it lost hold of cities in Iraq's western Anbar province. But the flight of al-Qaeda fighters raises the concern they can regroup elsewhere, as has often happened in the past.

Yassin Majid, an adviser to Prime Minister Nouri al-Maliki, said most of the leading insurgents had fled to the outskirts of Mosul or to a neighboring country amid the operations. Mosul is about 60 miles from the Syrian and Turkish borders.

"Operations will continue, and the Iraqi army will not leave Mosul until security and stability have been accomplished," he said.

Duraid Kashmola, the governor of Ninevah province, said the sweep that began Thursday would "not ease, for fear gunmen might return back in strength to the field." U.S.-backed Iraqi police and soldiers have been conducting raids on homes and have fanned out with checkpoints on city streets, though no clashes have been reported in the city, 225 miles northwest of Baghdad.

Interior Minister Jawad al-Bolani said 1,068 people had been detained in the last week, but 94 were cleared and released. Kashmola said most of those arrested were al-Qaeda members.

The assault on the Sunni al-Qaeda in Iraq group was launched after two other major crackdowns against Shiite militiamen in the southern city of Basra and the Baghdad district of Sadr City in the last two months. Those two sweeps continue, but uneasy truces with the powerful Shiite Mahdi Army militia have eased the heavy violence they sparked.

Bolani told a gathering of about 300 former Saddam Hussein-era officers in Mosul that the army and police would make room for them and that Maliki was urging them to return. Many in the crowd cheered the announcement.

Mosul's Sunni Arab population was once a major source of officers for Hussein's army, but many were removed because of their ties to his regime in a purge after the 2003 U.S. invasion. Their bitterness is believed to have fueled the Sunni-led insurgency.

Maliki traveled to Baghdad yesterday to meet with U.S. House Speaker Nancy Pelosi, who had been in the Mideast and made a surprise visit to Iraq. Pelosi, a top Democratic critic of the Iraq war, expressed confidence that expected provincial elections would be democratic and promote national reconciliation.