WASHINGTON (REUTERS) — A U.S. Army Black Hawk helicopter was shot down by small-arms fire in southern Iraq, killing seven people and wounding four onboard, a U.S. official said Wednesday.

The official at the Pentagon, speaking on condition of anonymity, said the helicopter was shot down near Kerbala, 50 miles south of Baghdad, early Thursday Iraqi time.

But Central Command in Tampa, Fla., issued a contradictory statement, saying the Black Hawk was downed at about 7:30 p.m. local time Wednesday and that initial reports put the number of people on board at six.

The Central Command statement said there was no confirmation of casualties.

There was no immediate explanation for the discrepancies in information from the Pentagon and from Central Command.

The Pentagon official said search-and-rescue personnel were at the scene where the craft came down, adding: ?They were pulling people out.? The Black Hawk had been carrying 11 personnel, the official said.

The Black Hawk was the second U.S. helicopter lost in combat since U.S. and British forces invaded Iraq two weeks ago. An Apache gunship went down last week, and its two crew members were captured by Iraqi forces.

U.S. planes battered targets in the center and outskirts of Baghdad early Thursday as the war entered a third week, with American troops just 19 miles south of the Iraqi capital.

U.S. war headquarters in Qatar said planes dropped almost 40 ?smart bombs? overnight on just one military storage facility in the Karkh district of Baghdad.

This correspondent heard a huge explosion in the city center which shook buildings at about 2 a.m. (6 p.m. EST Wednesday).

The explosion was followed by several loud blasts on the outskirts of the city, especially in the south, where Iraqi forces were preparing for the possibility of an assault by U.S. troops.

?It was one of the worst nights of bombing so far in Baghdad and the outskirts. There was the sound of warplanes all night,? said Reuters correspondent Nadim Ladki.

?The bombing went on all through the night, every 10 to 20 minutes,? he said. The war, which started March 20, entered its third week Thursday. Blasts resumed to the south and west of the capital following a two-hour lull around dawn.

Planes roared repeatedly over the city of five million.

It was not clear exactly where many of the blasts were. In the center, palaces belonging to President Saddam Hussein and Iraqi government buildings have been battered by the war.

The Pentagon said U.S. troops were 30 miles from Baghdad but a military source told a Reuters correspondent traveling with the 3rd Infantry that vanguard units were just 19 miles from the southern outskirts.

RAPID ADVANCE

U.S. forces smashed through elite Iraqi divisions Wednesday to close in on Baghdad, using fearsome air power to back the swiftest advance of the war.

The U.S. Central Command said it dropped almost 40 so-called Joint Direct Attack Munitions (JDAMS) — ?smart bombs? that home in on their targets by satellite navigation — on the Karkh storage facility Wednesday night.

?The regime, special security organization and possibly the special Republican Guard use the facility,? it said in a statement. ?These groups store critical military and security supplies for the regime in this building.?

Central Command also said that it also used the JDAMs on a farm used as a command and control facility at Radwaniyah, southwest of Baghdad, Wednesday.

The defenders of Baghdad have been preparing for urban warfare. Pick-up trucks equipped with machine guns and anti-aircraft guns are dotted across the city.

U.S. forces would like to avoid street fighting in Baghdad, which might take a heavy toll in military and civilian casualties. But planners believe this prospect is increasingly likely as Saddam prepares to stage his last stand in the city.