Renewed clashes pitting Iraqi rebels led by radical Shia cleric Moqtada Sadr against US-led forces continued in the southern city of Najaf on Sunday.
Sadr supporters continue to hold out in the city's holy mosque
US tanks and armoured vehicles appeared to be moving closer to the Imam Ali mosque, still held by the rebels after 18 days of fighting, witnesses said.
US planes have carried out more air strikes, punctuated by the sound of mortars and heavy machine-gun fire.
Correspondents say talks to end the stand-off seem to be going nowhere.
Elsewhere in Iraq:
- US military officials says four marines have been killed since Saturday in separate incidents in Anbar province, west of Baghdad.
- A US soldier is killed in a roadside bomb in the northern city of Mosul.
- French-American journalist Micah Garen is released by his kidnappers in the southern city of Nasiriya.
- Iraqi oil exports resume normal levels after a cut in output after threats to attack major oil installations.
- One Indonesian and two Iraqis are killed in an ambush in Mosul.
- The Iraqi interior ministry says 40 rebels were killed in fighting with US-led forces in Kufa, near Najaf. There has been no confirmation of the claim.
- A car bomb explodes in Baquba, 65km (40 miles) north of Baghdad, killing two people in an apparent attack against a local official.
About 1,000 unarmed Sadr followers are believed to be inside the Imam Ali shrine while armed fighters of the radical cleric's Mehdi Army militia roam the streets and Najaf's vast cemetery.
After repeated air strikes overnight on Saturday, US-led forces and Moqtada al-Sadr's militia fought battles in the street around the old city as the stand-off at the shrine continues.
The BBC's Alastair Leithead in Najaf says US forces appear to have edged closer to the Imam Ali mosque, and are perhaps 400 metres (yards) away as the crow flies.
However, our correspondent notes, to get any closer would mean entering the narrow alleyways of the old city - a location that is easier to defend than to attack.
No sign of endgame
Some civilians told reporters they were forming a human shield to deter attacks on the shrine.
Mr Sadr's whereabouts remain unclear.
A spokesman for Mr Sadr has said the cleric's militia will continue to protect the site from the outside, preventing any Iraqi and US troops from entering it.
An aide said on Saturday that talks on handing control of the shrine to Iraq's leading Shia authority, Grand Ayatollah Ali al-Sistani, had stalled.
Mr Sadr was asking for Ayatollah Sistani to send a delegation to take an inventory of precious items in the mosque, said the aide, Ali Smeisim.
He said Mr Sadr wanted to make sure his men could not be accused of
The BBC correspondent in Najaf says that negotiations appear to be going nowhere and that there is little sign of an imminent conclusion to the crisis.