A U.S. helicopter went down by gunmen's small arms fire in central Baghdad on Tuesday, an Interior Ministry source told Xinhua.

"I can confirm that a U.S. helicopter had come under fire in the Fadhel district around two hours ago and went down in a residential area of Sheikh Omer," the source said.

There is no further detail about the incident as the U.S. and Iraqi troops had cordoned off the area, he added.

Meanwhile, witnesses said that U.S. troops were patrolling in the heavily populated area with two helicopters hovering above when gunmen opened fire at one of the helicopters.

They added that the clashes erupted between gunmen and the U.S. patrol when more U.S. troops rushed to the area after the helicopter crashed.

The gunmen also opened fire at another helicopter during the clashes but they failed to hit the target, witnesses said. The U.S. military has not confirmed the incident yet.