BAGHDAD, April 5 (Reuters) - Heavy gunfire forced a U.S. military helicopter down in an insurgent stronghold south of Baghdad on Thursday, Iraqi witnesses said.

The U.S. military said it had no information on the reports.

Witnesses said the aircraft appeared to be an Apache attack helicopter. They said it came under attack near Latifiya, 40 km (25 miles) south of Baghdad.

"I saw a helicopter in the sky, then I heard heavy gunfire," said one witness. "I saw the helicopter move right and left before landing hard. It did not explode."

An Iraqi security official also said a helicopter had come down in the area. U.S. forces had closed off the site, witnesses said.

Insurgents shot down eight helicopters during a month-long period earlier this year, killing 28 people, mainly American soldiers. Six of those were U.S. military helicopters and two belonged to a private American security firm.

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