"Take cover, take cover," said a warning message played over loudspeakers by US occupation forces after the blasts.

"A rocket landed in an open parking lot in the Green Zone. There were no casualties and no damage to equipment was reported," a US military spokesman said, using the American name for the compound.

The rocket, apparently fired from across the Tigris, exploded in a parking lot near the Republican Palace, used by chief occupation administrator L. Paul Bremer and senior coalition staff, but caused no damage or casualties, he added.

The compound on the west bank of the Tigris river has come under rocket and mortar attack several times in recent months. 
 
Just over a week ago a bomber detonated half a tonne of explosives outside the US seat of power in Iraq, killing at least 20 people in the deadliest attack since the capture of Saddam Hussein.

Najaf attack
 
Earlier on Monday afternoon, the occupation headquarters in Najaf, south of Baghdad, also came under two rocket attacks.

According to Aljazeera's correspondent, "flames were seen rising from the headquarters" of the multinational forces which includes Salvadorian and Spanish troops.

Salvadorian troops are mainly
based at Najaf headquarters

The Spanish forces immediately carried out search campaigns and raided homes in nearby neighbourhoods.

The correspondent reported that ambulances and fire trucks belonging to the Iraqi civil defence forces in Najaf were prevented from entering the scene of the attack.

Casualties and the extent of the damage is not known, the correspondent added.

Iraqi civilians killed

Earlier on Monday, two Iraqi civilians were killed and another two injured when an improvised bomb exploded on a busy highway in Baghdad.  

The attack came after an Iraqi civilian was killed and two others seriously wounded late on Sunday in the northern city of Kirkuk after US troops opened fire on them, Iraqi police said.

The incident happened after occupation soldiers grew suspicious about a car parked near a block of government buildings and opened fire on it.

Earlier six Iraqi policemen were killed and several others injured in two separate rocket-propelled grenade attacks.

The attacks took place late on Sunday near Ramadi, a hotbed of anti-occupation attacks. An Iraqi checkpoint was also targeted, he said.

Search continues

US troops aided by Iraqis searched the Tigris river on Monday in northern Iraq for a soldier and two pilots
missing after a helicopter, searching for a capsized river patrol boat, crashed.

Five US helicopters have crashed
 in Iraq this month

Two Iraqi policemen and an Iraqi translator accompanying the US soldiers in the patrol boat were also killed in the incident, said a military spokeswoman.

The US military said the helicopter crash was not believed to have been caused by hostile fire, but investigations were underway.

A senior police official in Mosul said the 101st Airborne Division helicopter had flown at low altitude into cables strung across the river, which had swollen to higher than usual levels.

Fifth crash

Sunday's crash was the fifth involving a US helicopter in Iraq this month.

The helicopter disaster capped a black weekend for the US military, with six personnel killed in separate attacks.

But the US ground forces commander on Sunday flatly denied his troops were becoming bogged down in Iraq.

"I think what we're seeing overall across the country is a reasonable decrease in the number of engagements," Lieutenant General Ricardo Sanchez said.

UN decision

Meanwhile, UN Secretary-General Kofi Annan said he might decide as early as Monday on sending a mission to help a US handover of power to Iraqis.

Annan expects to decide on
sending mission to Iraq soon

"I would expect to make a decision in the next day or so," Annan told Swedish TV on Sunday as Washington said it saw a significant role for the UN in the handover of power to Iraqis in June, particularly in assessing the feasibility of elections. 

Annan has sent two security experts to Baghdad to decide whether it is safe for UN international staff to return to Iraq.

Washington, which previously ruled out any major UN political involvement in Iraq, has said the United Nations can help supervise the handover and discuss demands by the Shia and other Iraqis for early elections.

Top Shia cleric Ayat Allah Ali al-Sistani wants a full-scale election, which would probably favour the Shia.

A US plan envisages regional caucuses selecting an assembly to choose a transitional government for sovereignty in June. Washington believes elections would be difficult to organise due to lack of electoral registers and laws.