BAGHDAD -- U.S. and Iraqi forces began a series of operations on Tuesday targeting al-Qaida in Iraq after an upsurge in suicide bombings that U.S. commanders say are an attempt by the militant group to reignite sectarian violence.

"Working closely with the Iraqi security forces, we will continue to pursue al-Qaida and other extremists wherever they attempt to take sanctuary," said Lieutenant-General Raymond Odierno, in a statement announcing the start of the offensive, dubbed Operation Phantom Phoenix.

Odierno gave few details of the new offensive but said it comprised a "series of joint Iraqi and Coalition division- and brigade-level operations to pursue and neutralize remaining al-Qaida in Iraq and other extremist elements."

In a later statement, the U.S. military said it had killed three militants and detained 28 suspects in operations in Baghdad, the area just south of the capital and the northern Diyala and Nineveh provinces Monday and Tuesday.

Odierno, the day-to-day commander of U.S. troops in Iraq, did not say how Operation Phoenix would differ from current U.S. operations hunting al-Qaida operatives or what areas U.S. and Iraqi forces would target.

The U.S. military says al-Qaida has been badly damaged but has the capacity to carry out so-called "spectacular" attacks that cause mass casualties.