A US probe of an alleged massacre of civilians in Haditha, Iraq must go beyond accused Marines and up the military command to rule out any possibility of a cover-up, US lawmakers said.

US Marines raid a house during a night raid in the Iraqi town of Haditha, west of Baghdad, in 2005. A US probe of an alleged massacre of civilians in Haditha, Iraq must go beyond accused Marines and up the military command to rule out any possibility of a cover-up, US lawmakers said. [AFP]

"The test will be whether the leadership in the Department of Defense and in the administration does not try to ... say it was just a few Marines or a few soldiers, but looks to see if this is part of a larger systemic problem," Senator Jack Reed told "Fox News Sunday."

Meanwhile, Senator Carl Levin told CNN's "Late Edition" program: "There is a real possibility of a cover-up."

Levin pointed out that the massacre of some 24 men, women and children in November only came to light only months after the fact, in a March 2006 Time Magazine article.

Marines said in a press release the day after the incident that the Iraqis had been killed by a roadside bomb, but videotape footage showed children and elderly people had died of gunshot wounds.

"The press release that came out the following day was false," said Levin, the top Democrat on the Senate Armed Service Committee.

Another lawmaker said the incident is further proof of poor Pentagon leadership, and renewed his call for the resignation of Secretary of Defense Donald Rumsfeld.

"He should be gone," said Senator Joe Biden, the ranking member of the Senate Foreign Relations Committee.

Iraq's Prime Minister Nuri al-Maliki has denounced the killings in Haditha as an "odious crime" and called for talks "to redefine the obligations of coalition forces."

Reed, who serves on the Senate Armed Services Committee, said al-Maliki "is suggesting that this might be more comprehensive than just this one incident."

Senator Lindsey Graham told "Fox News Sunday" that he was "very confident" that the investigation would go as far up the chain of command as necessary.

"We're going to find out if ... the facts initially reported were wrong and why were they wrong, did people know better and tell a lie, should people have known better and investigated harder rather than letting it sit, did people actually pull a trigger and kill a child who was innocent of any wrongdoing.

"All those things are going to be looked at, and it will go where it goes," the South Carolina Republican said.

"I'm very confident that the military legal system and Marine Corps will handle this appropriately," Graham said, and compared it to investigation of prisoner abuse at Abu Ghraib prison outside Baghdad.

"As to Abu Ghraib, dozens of officers have had their careers ruined, most, I think, appropriately so. And we will see if Abu Ghraib is a done deal after the prosecution of the dog handlers or there are more people involved."

Secretary of State Condoleezza Rice, who made the rounds of Sunday talk shows, said the Haditha case was being handled "at the highest levels" and promised a "serious and thorough investigation."

"That's what democracies do when there are allegations of misconduct," she told CNN." And when those investigations are finished, I'm sure that there will be appropriate punishment if people are indeed found guilty."

The US officials' remarks to the Sunday morning talk shows came after a military inquiry in Fort Meade, Maryland last week cleared US forces of wrongdoing during a raid on the village of Ishaqi north of Baghdad, on March 15, in which four people died.