US marines were still bogged down on Monday outside the southern Iraqi city of Nassiriya, the key to opening a second route north to Baghdad, after taking significant casualties there on Sunday.
Reuters correspondent Sean Maguire said the Marines he was travelling with were stuck and had to decide whether to fight through to Nassiriya's bridges over the Euphrates river about 375 km southeast of Baghdad, or go around the city.
"We can see Nassiriya but we're not moving. Commanders fairly high up the chain are deciding what we should do," Maguire said, speaking from about 20 km from the city. "The whole regiment we're travelling with is just stuck here."
He said there had been no action since US artillery fire on the city on Sunday evening. "Either they have to get stuck in and fight their way through or go round -- but it is a long, awkward way round. They need those bridges," he said.
US officers said on Sunday that the Marine battalion heading the fight suffered "significant casualties" in a battle with irregular guerrilla fighters known as Saddam's Fedayeen.
US troops captured the northern ends of the two bridges in the east of Nassiriya early on Sunday, opening the way for forces to head north toward the Tigris river and Baghdad.
But units of the Fedayeen, an irregular militia force of loyalists to Iraqi President Saddam Hussein, counterattacked. US officers suggested late on Sunday that the bridgeheads were now secure but the area in between was not.
"This is one of few urban centres they really have to touch. A relatively small group of guerrilla fighters can hold up a whole brigade," Maguire said.
US Army general John Abizaid told a news conference in Qatar on Sunday that 12 US service members were missing after an ambush in the Nassiriya area and said up to nine were killed in the "sharpest engagement of the war thus far".
Iraq displayed five shaken US soldiers apparently captured in the ambush near Nassiriya and also filmed the bloodied bodies of up to eight men they said were dead American soldiers.
A CNN television correspondent at Nassiriya on Sunday quoted eyewitnesses in the battle as saying they had seen about 10 American bodies around an amphibious assault vehicle that had been hit by a rocket-propelled grenade.
Iraqi defence officials said 25 bodies of US soldiers had been found on the battlefield at Nassirya.
Iraqi Information Minister Information Minister Mohammed Saeed al-Sahaf said on Sunday that foreign invaders headed to Nassiriya had been "taught a lesson they will never forget".
Speeding columns of the US Third Infantry have covered nearly two thirds of the 500 km from the Kuwaiti border in two days before running into Iraqi resistance near Najaf on the southwest bank of the Euphrates.
A strike north across the river at Nassiriya towards the Tigris river and Baghdad could create a pincer movement.