Fresh explosions rocked the outskirts of Baghdad this afternoon as the Iraqi capital came under renewed air attack, reporters in the city have said.
About a dozen blasts were heard in the distance, in the roughly the same area where Iraqi troops are believed to be dug in to defend the city from US and British ground forces approaching from the south.
Baghdad has been hit by waves of fierce air strikes through today as a heavy sandstorm whips through the city.
US aircraft have been attacking units of Saddam Hussein's Republican Guard just outside Baghdad for the first time.
Warplanes and helicopters took part in the attack on the Iraqi positions, in what correspondents say is a sign the battle for the capital has begun.
US ground forces are also understood to be attacking Republican Guard positions while bombers attack them from the air.
A British defence official said the bombardment began last night. Distant explosions were heard in Baghdad, but it was not clear if these were part of the air strikes against the Medina Division of the Republican Guards facing US columns that have reached the Kerbala area, 60 miles from the capital. Several explosions also rocked Baghdad's outskirts.
But US military commanders are concerned that persistent sandstorms forecast for the Baghdad region could hinder their advance.
The US military yesterday acknowledged losing one helicopter and Iraqi television showed two men it said were the crew.
A senior Pentagon source said he could not confirm US media reports that Iraqi leaders had drawn a "red line" around Baghdad within which Republican Guard had been authorised to used chemical weapons. Iraq denies that it has such weapons.
At least 30 Iraqis who may have been on their way to reinforce the city of Nassiriya were killed today in what appeared to be a bombing raid by US-led forces, a Reuters correspondent said.
He said that he counted 20 dismembered bodies by a wrecked bus about 12 miles north of the key riverside city in southern Iraq and at least 10 more fresh corpses in the wreckage of another bus, two trucks and two cars.
All seemed to be men and the all the vehicles were facing in the direction of Nassiriya.
Elsewhere, sixteen civilians have been killed and another 95 wounded in allied bombing of Baghdad and other Iraqi cities overnight, the Iraqi Information Minister said today.
US commanders say the invasion is going according to plan and that some casualties were inevitable. But Iraqi Deputy Prime Minister Mr Tareq Aziz told a news conference that President Saddam Hussein was "in full control of the army and the country".
Mr Aziz ridiculed US hopes that invading troops might be greeted with flowers. "We do not have candies to offer. We are just offering them bullets," he said.
The US and British forces have faced stiff resistance from Iraqi forces in towns including Nassiriya, Basra and Umm Qasr.
But the crucial port of Umm Qasr is now "under total control", according to British forces.
"The clean-up operation is over," a British officer said.
US and British officers see Umm Qasr and Basrafurther north as vital components in a plan to establish ahumanitarian aid corridor for non-governmental organisations to deliver aid to the rest of the country.
Warnings intensified of a humanitarian crisis as fighting in the south prevented US-led forces from gaining control of ports vital for shipping in supplies. Aid and water are growing short in Iraq's second city, Basra.
In New York, UN Secretary-General Kofi Annan called for urgent action to ensure there was enough water in Basra, a city of some two million people.