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BAGHDAD, April 29 (Reuters) - The U.S. military in Iraq launched an artillery barrage in southern Baghdad on Sunday against suspected insurgent targets, with two dozen loud explosions shaking the southern outskirts of the capital.

U.S. military spokesman Lieutenant-Colonel Christopher Garver said the morning blasts, which were heard across the city, were caused by U.S. artillery but declined to say what the target was.

Tens of thousands of U.S. and Iraqi troops have been deployed in Baghdad as part of a 10-week-old security crackdown to combat sectarian militias and insurgents.

The Iraqi police said the artillery was being fired from the U.S. Forward Operating Base Falcon in southern Baghdad into the al-Buaitha neighbourhood of Dora, a volatile district that is a Sunni insurgent stronghold.

U.S. military commanders say insurgents, including Sunni Islamist group 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.

Artillery blasts have been heard in the evenings but they are rare in the daytime.

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