BAGHDAD, Feb 1: US troops opened fire to quell a riot at a military run prison in southern Iraq on Monday, killing four inmates and wounding six, military authorities said.

The disturbances erupted during a routine search of part of the inmate area at Camp Bucca prison, near the border with Kuwait, a statement said. An investigation into the riot was under way, but Lt Col Barry Johnson, a spokesman for US military prison operations, said there was "no direct" link to the country's election on Sunday.

All of the dead and injured were Iraqi, Col Johnson said. "Some third country nationals are held at Camp Bucca but they were not involved in the disturbances." The troubles lasted about 45 minutes before US troops opened fire, according to the military.

"The violence erupted after a routine search for contraband in one of the camp's 10 compounds," said the statement. "The riot quickly spread to three additional compounds, with detainees throwing rocks and fashioning weapons from materials inside their living areas."

The military said that after unsuccessful attempts to quell the violence with warnings and "non-lethal force", guards engaged the detainees to quell the riot. "The cause of the riot and use of lethal force is currently under investigation by the chain of command and the US army's Criminal Investigations Division," the statement said.

The US military says it holds an estimated 7,000 security internees, with 4,700 of those held at Camp Bucca, near the port of Umm Qasr, and 2,300 at the now infamous Abu Ghraib prison, west of Baghdad.

Iraqis seek answers: US guards should be put on trial if found to have used excessive force to quell a riot at a military camp in which four detainees were shot dead, Iraq's human rights minister said on Tuesday.

Bakhtiar Amin said he believed two US troops had opened fire on rioters but he did not know why. His ministry had sent a delegation to the camp in southern Iraq to investigate.

"If there is a mistake, then those in charge should be brought to account," Amin told Reuters. "If we are convinced there was no justification for the degree of force used then we want them to be tried," he added. "That is what the American side says as well."

Jordanian militant Abu Musab al Zarqawi's group, al Qaeda in Iraq, threatened retaliation for the killings in an Internet statement titled "About the Muslim prisoners in Basra".

"What was the fault of defenceless prisoners ... that you should treat them like this?" the statement said. "Tyrants of the age, we will not let these crimes of yours pass - we will settle the score." -Reuters