BAGHDAD, May 10 (Reuters) - A U.S. air strike killed three militants in Baghdad on Thursday during a raid targeting cells suspected of smuggling in sophisticated bomb making components from neighbouring Iran, the U.S. military said.

It was the third major raid in a week in Sadr City, the stronghold of the Mehdi Army militia of anti-U.S. Shi'ite cleric Moqtada al-Sadr, in search of militants accused of procuring so-called explosively formed penetrators, or EFPs, from Iran.

EFPs are a particularly lethal type of roadside bomb that can destroy a battle tank.

The U.S. military said in a statement that ground forces came under small arms fire from two separate buildings at the start of the raid in Sadr City.

"Despite efforts to subdue the armed terrorists, Coalition Forces continued to receive enemy fire," the statement said.

"Using appropriate escalation of force to react to the perceived threat, Coalition Forces called for close air support, killing three armed terrorists," it added, without saying if attack helicopters were used.

The military said three civilians were hurt in the raid, which residents said took place before dawn. Four militants were detained.

Attacks on U.S. troops using EFPs have increased, reaching 65 attacks in April, according to media reports quoting Lieutenant-General Raymond Odierno, commander of day-to-day operations in Iraq.

Washington accuses Iran of fomenting violence in Iraq. Tehran denies the charge and blames the chaos in the country on the U.S.-led invasion in 2003.

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