Iraq ? Nearly 6,000 Sunni Arab residents of the northern city of Hawija joined a security pact with American forces Wednesday in what U.S. officers described as a critical step in plugging the remaining escape routes for extremists flushed from former strongholds.

The new alliance – called the single largest single volunteer mobilization since the war began – covers the “last gateway” for groups such as al-Qaida in Iraq seeking new havens in northern Iraq, U.S. military officials said.

U.S. commanders have tried to build a ring around insurgents who fled military offensives launched earlier this year in the western Anbar province and later into Baghdad and surrounding areas. In many places, the U.S.-led battles were given key help from tribal militias – mainly Sunnis – that had turned against al-Qaida and other groups.