Five US soldiers have been captured and paraded on Iraqi television, on what American commanders said was the toughest day of fighting since war began. Two British soldiers have also gone missing in southern Iraq, the UK Ministry of Defence said on Monday. Central Baghdad was hit by several large explosions early on Monday, as ground forces continued to meet resistance in the push to the capital.

US Marines suffered up to 10 dead and 14 wounded in heavy fighting with Iraqi forces in and around the southern city of Nasiriya, US commanders said.

Further north, US forces are investigating a suspected chemical plant about 160 kilometres (100 miles) south of Baghdad.

A US military spokesman at Central Command in Qatar said simply: "We have identified potential sites of interest and we're looking into (them)".

Heavy fighting has also erupted at Karbala, about 80 kilometres (50 miles) from Baghdad

A CNN reporter said US helicopter gunships attacked a division of Iraq's Republican Guard there and were met with heavy anti-aircraft fire.

Earlier, the US military confirmed that a six-vehicle supply convoy was ambushed near Nasiriya by Iraqi troops, and that 12 of its personnel were missing.

Iraqi television broadcast pictures of the bodies of several American soldiers and their wrecked vehicles, as well as interviews with five captured survivors of the ambush - one of them a woman.

The Iraqis say they have killed 25 Americans in the area and destroyed 30 tanks and armoured vehicles across southern Iraq. Iraqi losses, both in Nasiriya and throughout the country, are unclear.

The suspected Iraqi chemical plant under investigation is near the holy town of Najaf.

US Army General John Abizaid of US Central Command said top Iraqi generals had been questioned about chemical weapons.

"We have an Iraqi general officer, two Iraqi general officers that we have taken prisoner and they are providing us with information," he told reporters in Qatar.

The BBC's Peter Hunt in Qatar says it would be a great propaganda coup for the coalition forces if the suspected plant was found to be producing chemical weapons.

General Abizaid said Sunday had been the "toughest day of resistance" so far for the US forces.

But he insisted: "We are on track. We will arrive in the vicinity of Baghdad soon."

He described the broadcast of footage of dead and captured American soldiers, carried round the world by the Arabic television news channel al-Jazeera, as "disgusting".

Iraq's Foreign Minister Naji Sabri told the BBC that Iraq would not harm the prisoners.

American units are still engaged in fierce fighting in Nasiriya, a key crossing point on the Euphrates River, and other areas of southern Iraq.

The southern Iraqi port of Umm Qasr also saw renewed fighting on Sunday, after US Marines found a large group of Iraqi soldiers there - some of whom are thought to have been from the elite Iraqi Republican Guard.

In other developments:

* In northern Iraq, there has been heavy fighting to the south of the city of Irbil

* The International Red Cross warns of a humanitarian emergency in Basra. A spokesman tells the BBC that water and electricity supplies to the city have been cut off

* US President George Bush says he expects a massive humanitarian aid programme for Iraq to begin within the next two days

* In Kuwait, the defence ministry says an Iraqi missile was intercepted by a Patriot missile in the north of the emirate on Sunday

* The US accuses Russian companies of selling arms to Iraq in breach of United Nations sanctions

* Coalition military spokesmen deny any of their planes are missing over Baghdad, despite rumours that two parachutists were seen coming down into the River Tigris

* The two crew of a British RAF Tornado aircraft are confirmed dead after being shot down by a US Patriot missile near the Kuwaiti border

PHOTO CAPTION

This image from Iraqi television on March 23, 2003 shows the body of a U.S. soldier after a battle southeast of the southern Iraqi city of Nassiriya where U.S. forces have encountered stiff resistance. Photo by Reuters (Handout) - Mar 23 4:34 PM ET