It was the fifth US helicopter lost in Iraq this month -- three from hostile fire.
Strong explosions reverberated through the heart of this troubled capital about 10:35 p.m., followed by sirens and a recorded message warning those in the coalition headquarters compound known as the "green zone" to take cover.
A coalition official said at least one rocket, apparently fired across the Tigris, exploded in a parking lot near the Republican Palace, used by America's top civilian administrator in Iraq, L. Paul Bremer III, and senior coalition staff, but it caused no damage or casualties.
The attack occurred three days after a UN security assessment team arrived in Baghdad to determine whether it is safe for the organization's international staff to return to Iraq.
Secretary General Kofi Annan withdrew the international staff last year following two vehicle bombings at the UN headquarters in Baghdad, including the Aug. 19 attack that killed 22 people, among them the top UN envoy, Sergio Vieira de Mello.
The attack on the green zone took place a day after the seven policemen were slain in two separate attacks at checkpoints around the city of Ramadi, 70 miles west of Baghdad in the Sunni Triangle, a center of resistance to the US-run occupation. Iraqi police who reported the attacks made no mention of any insurgent casualties.
Attacks against US forces and their Iraqi allies have persisted despite the Dec. 13 arrest of Saddam Hussein, who was captured near his hometown of Tikrit. Many of the victims have been Iraqi civilians.
An Iraqi man was killed yesterday when he stepped on a roadside bomb as he got off a bus in a Baghdad suburb, Iraqi Civil Defense Corps Second Lieutenant Mustafa Tariq said. The explosion wounded three passengers, one critically, and destroyed the bus, he said.
Last night, a roadside bomb exploded in a west Baghdad neighborhood, wounding one civilian and damaging at least three vehicles, witnesses said.
Elsewhere, two projectiles exploded for a second straight day yesterday at the US military base in Kirkuk, Iraqi police said, but there were no reports of damage or casualties. Witnesses also reported explosions near a Spanish garrison outside Najaf, but the Spanish Defense Ministry said the base was not attacked.
