(CNN) -- A U.S. Army Black Hawk helicopter was shot down by small arms fire Wednesday night in south-central Iraq, military officials said, but there were conflicting reports on casualties.

The Pentagon said seven soldiers were killed and four others wounded and rescued. But a statement from U.S. Central Command headquarters in Qatar said only six people were on the Black Hawk and that casualties could not be confirmed.

The Central Command statement said the chopper crashed around 7:30 p.m. (10:30 a.m. EST).

Col. Tom Bright, the Marine Corps chief at the U.S. Central Command's joint operations center in Qatar, said an investigation has been launched into what happened.

The crash happened near Karbala, about 50 miles from Baghdad. The city has seen heavy fighting in recent days between coalition forces and Iraqi Republican Guard units.

Meanwhile, a U.S. Navy F/A-18C Hornet went down over Iraq early Thursday. A search-and-rescue operation has been launched, U.S. officials said. The single-seat fighter jet from the USS Kitty Hawk went down around 12:45 a.m. Thursday (3:45 p.m. ET Wednesday). Further details were not immediately available.