The announcement came on a day US troops poured into the Louisiana city of New Orleans with shoot-to-kill orders to scare off looting gangs and enable rescuers to help thousands of people stranded by Hurricane Katrina.
Faced with a growing threat of anarchy after a natural disaster that may have killed thousands of people, the US military on Friday rushed in National Guard reinforcements.
Armed looters have had the run of this famed city of jazz musicians and French Quarter bars since Katrina pounded the US Gulf Coast on Monday, but they were warned not to push their luck.
"These troops are battle-tested. They have M-16s and are locked and loaded," Louisiana Governor Kathleen Blanco said on Thursday night of one group of 300 National Guard troops being deployed here after recent duty in Iraq. "These troops know how to shoot and kill and I expect they will."
The post-Hurricane Katrina petroleum-supply outlook improved somewhat on Friday as US and European governments agreed to release more than 60 million barrels of oil and refined products from their emergency reserves.
The governments of 26 countries agreed to release the equivalent of two million barrels of oil per day from strategic reserves to cope with the aftermath of Hurricane Katrina, the Paris-based International Energy Agency said.
Most residents are desperate for an end to the violence and a crackdown on looters was ordered when it became clear the looting and gunfire were hurting relief efforts.
Bodies rotted away on busy streets, armed men opened fire on troops and rescue workers, and seriously ill people braved the floodwaters in wheelchairs to search for help.
Officials said the toll was certainly in the hundreds and probably in the thousands, but details remained sketchy.
Dead bodies are lying in the
streets of the devastated city
"Call it biblical. Call it apocalyptic. Whatever you want to call it, take your pick," said 46-year-old Robert Lewis.
He was rescued as floodwaters invaded his home and endured two days of diabolical conditions at a shelter before finally being evacuated to Houston.
"There were bodies floating past my front door. I've never seen anything like that," he said, near tears from apparent emotional exhaustion.
Pentagon officials said an additional 4200 National Guard
troops would be deployed over three days and that 3000 regular army soldiers may also be sent in to tackle the armed gangs that have looted stores across New Orleans.
"We will not tolerate lawlessness, or violence, or interference with the evacuation," Secretary of Homeland Security Michael Chertoff said.
The reinforcements mean nearly 50,000 part-time National Guard and active-duty military personnel are being used in the biggest domestic relief and security effort in US history.
President Bush urged Americans
to conserve petrol
But the deployment has so far failed to guarantee an effective rescue plan and many of Katrina's victims are increasingly frustrated at being left to fend for themselves.
Under pressure from some Democrats for allegedly acting too slowly and for cutting federal funding for improvements to New Orleans' levees, US President George Bush was to visit the city on Friday.
The US Senate approved his request for $10.5 billion in emergency disaster relief late on Thursday, with billions more in aid seen passing Congress in coming weeks.
The help cannot come quick enough in New Orleans, known to those who love it as the Big Easy.
Flooded city hospitals had no electricity and critically ill patients were dying because they no longer had access to oxygen, insulin or other medicines.
Doctors worked around the clock to keep patients alive and evacuate them but logistical arrangements were chaotic and made worse by the violence. At one hospital, evacuation was called off when an armed man opened fire on doctors and soldiers.
New Orleans is short of food,
water and medical supplies
Shelters set up to care for thousands of evacuees in New Orleans were still without food and water early on Friday and families slept near corpses and piles of human waste.
Lake Pontchartrain's muddy floodwaters still own New Orleans four days after bursting through the levees that once protected it, and now they are toxic with fuel, battery acid, gas, garbage and raw sewage.
Disease and chaos
Health experts warn outbreaks of disease could wreak havoc in the days and weeks ahead.
The misery belied New Orleans' romantic and carefree image, and instead left it looking more like a Third World trouble spot in the midst of a major refugee crisis.
Thousands of people were finally evacuated from the city on Thursday night and taken to the Astrodome stadium in Houston, about 563km west, but it quickly filled up and police turned away busloads of the evacuees to other shelters.
Katrina forced hundreds of thousands of people from their homes and shut refineries along the Gulf Coast shut, sending petrol prices at the pump soaring to new records of well over $3 a gallon in most parts of the country.
Bush urged Americans to conserve petrol to help overcome the crisis. "Don't buy gas if you don't need it."