(Adds U.S. military statement)

BAGHDAD, April 20 (Reuters) - U.S. forces killed two gunmen after a patrol came under fire from a mosque in a Shi'ite neighbourhood of Baghdad on Friday, the U.S. military said.

"A patrol performing routine security operations around the area took small arms fire from the mosque and requested air support ... to come and assist them," U.S. military spokesman Lieutenant-Colonel Scott Bleichwehl said.

The incident, which Bleichwehl said lasted for about 90 minutes, took place in the southwestern Shi'ite neighbourhood of al-Bayaa before weekly Friday noon prayers.

A source at Yarmuk hospital said six people were wounded in the attack, including a woman.

The wounded were saying a U.S. attack helicopter had fired near the mosque, the hospital source said. Local media also said a U.S. helicopter had attacked a mosque in the al-Bayaa area.

The U.S. military initially said the helicopters had not opened fire, but later issued a statement saying: "Attack aviation helicopters fired approximately 100 rounds of 30 mm ammunition during a firefight near a mosque."

A Reuters journalist saw bullet holes in the mosque's walls but no sign that it had been fired on by a helicopter.

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