Two separate US military investigations into the Iraqi civilians' deaths are nearing an end, but allegations that US Marines gunned down Iraqi civilians have prompted widespread concern in the United States.
Democratic Representative John Murtha told ABC News' "This Week" program that the military had sought to "cover-up" the Iraqis' deaths and "stifled" an initial probe into the November 19 killings.
On the same program, Senator John Warner, the Republican chairman of the Senate Armed Services Committee, said he would treat the matter like the Abu Ghraib scandal and hold congressional hearings into the incident.
US defence officials said on Friday that the probes into the killings were nearing an end and that Defence Secretary Donald Rumsfeld had been briefed on the investigations.
One criminal investigation is into the deaths and a second administrative inquiry is looking at whether the Marine unit involved tried to "cover-up" events.
Murder charges possible
Time magazine reported Sunday that lawmakers were told in briefings last week that some members of the Marine unit involved may soon face charges as serious as murder.
What is not in dispute is that 24 Iraqi civilians in the town of Haditha died on November 19 shortly after a US soldier was killed by a roadside bomb.
Five Iraqis were killed fleeing a taxi, including a taxi driver and four students, while another 19 men, women and children were killed inside or around four homes as members of the US Marines' Kilo Company moved through the town, according to media accounts.
"This is going to be an ugly story," Republican Representative John Kline, a former marine, told Time magazine, in an article published on Sunday.
"This was a small number of Marines who fired directly on civilians and killed them," said Congressman Kline, who has been briefed on the incident by military officials.
Asked if he believed there had been a cover-up, Congressman Murtha, a prominent critic of the US administration over the Iraq war, told ABC: "No question about it."
"We don't know how far it goes. I mean, it goes right up the chain of command, right up to General Pace. When did he know about it?" Congressman Murtha questioned, referring to the chairman of the US Joint Chiefs of Staff, Marine General Peter Pace.
General Pace is the America’s top military officer and a senior advisor to Mr Rumsfeld.
Pace accused
"Who ordered the cover-up? I'm sure he (Pace) didn't, but what ... who said, we're not going to publicise this thing?" Congressman Murtha said.
"Until March, there was no serious investigation. There was an investigation right afterwards, but then it was stifled," the lawmaker claimed.
Lieutenant General John Sattler, the marine commander who would decide whether to pursue charges against any marines, has not yet received the findings of a criminal investigation into the Haditha case, a marine official said.
Reports about the killings come as the US military is still trying to shake off the adverse publicity it received over the abuse of Iraqi detainees at Abu Ghraib prison outside Baghdad.
Recent polls show a majority of Americans now believe the Iraq war was a mistake, but it remains to be seen how the Haditha incident will play on the domestic front here.
Some news reports, however, have pointed out that the revelations over the My Lai massacre during the Vietnam War, when US soldiers killed unarmed villagers, sparked a decline in public support for that conflict.