BAGHDAD: US troops captured 72 suspected insurgents and seized nitric acid and other bomb-making materials in overnight raids on al Qaeda in the north and west of Baghdad, the US military said on Sunday.
The synchronised operations took place in the provinces of Anbar and Salahaddin, both Sunni Arab strongholds.
In the city of Samarra alone, 36 people with links to al Qaeda in Iraq were arrested. In Karmah, near the insurgent bastion of Falluja, US forces confiscated 20 drums of nitric acid and other bomb-making materials.
Insurgents have been shifting tactics in recent months and have rigged nearly a dozen truck bombs with chlorine gas, mainly in western Anbar province.
The US military commander in Iraq, General David Petraeus, has called al Qaeda "probably public enemy number one" in Iraq and said the Sunni Islamist group was bent on committing what he called "sensational" attacks designed to fuel sectarian violence.
Earlier on Sunday, the US military launched an artillery barrage in southern Baghdad against suspected insurgent targets, with two dozen loud explosions shaking the southern outskirts of the capital.
US military spokesman Lieutenant-Colonel Christopher Garver said the morning blasts were caused by US artillery but declined to say what the target was.
Tens of thousands of US and Iraqi troops have been deployed in Baghdad as part of a 10-week-old security crackdown to combat sectarian militias and insurgents.
US military commanders say insurgents, including al Qaeda, have regrouped in Baghdad's outlying areas to launch attacks and build car-bombing networks that have caused mass casualties in recent weeks.
