President George W Bush has declared a "major strategic shift" in Iraq following the US troop surge.
He said the US now held the initiative and was looking to deliver a "crippling blow" to al-Qaeda in the country.
US troop levels in Iraq are now due to be reduced by about 20,000 by July, but Mr Bush said after that, the "drawdown" process would be frozen.
Then, he said, senior commander General David Petraeus would have "all the time he needs" to assess the next step.
Gen Petraeus had called for a 45-day "period of consolidation and evaluation" after July, before any more troops left.