Washington has projected the withdrawal of five units by July, which would bring the number of US troops in Iraq down from a current 160,000 to about 130,000- the level before a "surge" was launched last February.
Speaking Wednesday in Owesat village on the banks of the Euphrates, about 25 kilometres southwest of Baghdad near the town of Yusufiyah, Petraeus vowed no quarter would be given in the fight against Osama bin Laden's extremist network, blamed for much of the violence in Iraq.
"We cannot let up- they are much more on the defensive right now than they have been in years and that is where we have to keep them," Washington's top general in Iraq said as he declared the village of Owesat, just months ago a hotbed of Sunni insurgency, now secure.
"This was a small Al-Qaeda sanctuary that offered an opportunity to go right across the river and right into Baghdad," he said.
"Having this secured is very important to the overall security of the Iraqi capital."
He shrugged off concerns that the US troop withdrawals could see a reversal of gains made in the past six months, when according to US figures, the number of attacks across Iraq has dropped by 62 per cent.
"The official Iraqi security forces has increased by something like 110,000 or so in the past year- during which (time) our surge was 30,000," he said after visiting the rural village, reaching it on foot by crossing a floating bridge the US military has constructed across the Euphrates.