The Iraqi prime minister on Saturday sealed the northern border crossing into Syria and imposed a dusk to dawn curfew in the region around the Rabiaa frontier post.
The order went out as Iraqi forces, backed by American soldiers, swept into Tal Afar, an insurgent stronghold about 100 kilometers (60 miles) to the east.
The order by Prime Minister Ibrahim al-Jaafari was read on Iraqi television by Interior Minister Bayan Jabr.
The decree closed the border to all transportation, including the railroad, except for vehicles with special permission from the Interior Ministry.
Iraq and the United States have both complained bitterly that Syria has not done too little to block the flow of so-call foreign fighters into Iraq across the long and porous border.
Jabr said the closure was in effect under further notice, AP reported.