Heavy fighting has continued for a third day between Shia militias and the Iraqi security forces in southern Iraq.
There are reports of extensive exchanges of fire between the Iraqi army and militiamen in Basra and in the town of Hilla, just south of Baghdad.
More than 70 people have died and hundreds have been injured in days of violence sparked by an Iraqi crackdown on Shia militias in Basra.
Iraqi PM Nouri Maliki vowed to fight Basra's Shia militias "until the end".
"We have made up our minds to enter this battle and we will continue until the end. No retreat," said Mr Maliki in a speech broadcast on Iraqi state television.
On Wednesday, the prime minister, who has personally overseen the operation in Basra, gave Shia militants there 72 hours to lay down their arms or face "severe penalties".
The leader of the Mehdi Army, Shia cleric Moqtada Sadr, has spoken of the possibility of negotiations to end the violence.
In Basra, police chief Adbul Jalil Khalaf said he survived an assassination attempt overnight, in which three of his bodyguards were killed.
Residents in the city have said that they are beginning to run out of food and water.
One told the BBC that the Iraqi army broke into shops, took food and water, then set fire to shops and cars on the street.
"I am trying to look out of the window now, but I can't - the smoke's really heavy and smells really bad. Everything is burnt," he said.
An oil pipeline near Basra, which carries oil for export, was damaged by a bomb.
A Southern Oil Company official told Reuters news agency the main pumping station of Zubair 1 had been shut down and that exports would be greatly affected.
In other developments across the country:
The FBI said it had recovered the bodies of two US security contractors kidnapped in Iraq in 2006
A prominent civilian spokesman for the Baghdad security operation, Tahseen Sheikhly, a Sunni who often appeared with US officials at news conferences, was kidnapped by gunmen from his home in the capital
Thousands of Sadr supporters gathered in Baghdad's Sadr City, a vast Shia-dominated suburb, to demand Mr Maliki's resignation over the military operation
Baghdad's fortified Green Zone was again hit by several rounds of rockets, causing a fire, Iraqi and US embassy officials said
Iraqi police in Kut said dozens of people were killed in clashes on Thursday between Iraqi and US forces, and Shia militiamen, the AFP news agency reported
There have also been clashes through the night and the early morning in the towns of Hilla and Diwaniya
The number of gunfights in southern Iraq appears to be growing, says the BBC's Crispin Thorold in Baghdad.
The fighting still seems to be mainly with members of the Mehdi Army, our correspondent says.
The Medhi Army had held to a ceasefire since last August, contributing to the general fall in violence across Iraq.
Baghdad's Green Zone has been targeted by insurgents again
It is not clear what has prompted the government crackdown at this time. The government says its campaign aims to re-impose law and order in Basra.
However, Sadrists say the government is attempting to weaken the militias before local elections scheduled for October.
At stake, analysts say, is control of Iraq's only port city and the region's oil fields.