Iraq says a major operation is under way to try to retake the northern town of Talafar from insurgents.
US and Iraqi troops swept through the town, smashing walls with armoured vehicles and engaging in gun battles.
The Americans believe the town is being used as a staging post by foreign fighters crossing into Iraq from Syria.
Iraq's defence minister said 144 rebels had been killed in Talafar in the past two days. He said his forces were ready to strike rebels in four other towns.
Iraqi Prime Minister Ibrahim Jaafari said action had to be taken in Talafar because insurgents were trying to isolate it from the rest of Iraq and the political process.
"At 0200 [local time] today, acting on my orders, Iraqi forces commenced an operation to remove all remaining terrorist elements from the city of Talafar," Iraqi Prime Minister Ibrahim Jaafari said in a statement.
The US military drove the insurgents out of Talafar a year ago, only for them to return once the troops had withdrawn.
Watch video of the latest fighting including the 'claimed' shooting down of a US helicopter here BBC
This is the biggest military operation in Iraq for almost a year
So round and round we go , whats to bet that a week from now the soldiers will pull out and a month after that the insurgents will return . Each time more innocent civilians will die ,