The US Senate will hold hearings soon into an alleged massacre of Iraqi civilians by US Marines, a committee chairman said Tuesday as Republicans and Democrats said they were deeply upset about the accusations. "We've got our duty, and we'll do it. We'll go wherever the facts lead," Sen. John Warner, the Senate Armed Services Committee chairman, said. Warner, a venerable Republican in the Senate, is a former secretary of the Navy, which made him head of the Marine Corps. Warner was upset over reports that Marines killed up to 24 Iraqi civilians last November in the town of Haditha without cause, then engaged in a cover-up to keep the facts from surfacing. Warner told reporters he wanted to hold the first of what he expected would be a series of hearings on the allegations after Army Maj.-Gen. Eldon A. Bargewell has completed his investigation into whether military personnel lied about what occurred at Haditha. Warner said Bargewell probably would be the first witness called. Congressional aides say Bargewell's report could be completed within the week, but the military's separate criminal investigation is not expected to be finished soon. In a letter to Defense Secretary Donald H. Rumsfeld, Warner requested the Pentagon on Tuesday tell him "the earliest possible date that the department could provide witnesses" for the first hearing. Warner stressed that delaying the results of such investigations will mean that "a mixture of information, misinformation and unconfirmed facts will continue to spiral in the public domain." "We must do everything possible to prevent our military personnel, and indeed the values of all our military services, from being judged on unofficial information in the court of public opinion prior to the conclusion of official investigations," Warner wrote. His counterpart in the House of Representatives, Republican Representative Duncan Hunter also has pledged to hold hearings in the House Armed Services Committee. But he, too, has said he wants to wait until the military has completed its investigations to ensure Congress doesn't interfere with potential criminal proceedings. Over the past week, more details have emerged about the November incident, and a senior US defense official said military investigators have evidence that points toward unprovoked murders by Marines. Politically, the alleged murders in Haditha - as well as unsubstantiated claims of unprovoked civilian deaths by US troops elsewhere in Iraq - threaten to drag support for the Iraq war down further and could turn into another political problem for President George W. Bush and Republicans five months before congressional elections. Polls show voters increasingly uncomfortable with the direction of the war and more inclined to see Democrats leading Congress. Returning to Washington after a weeklong Memorial Day break, lawmakers expressed grave misgivings about Haditha and said the allegations could further tarnish the US image abroad and hurt efforts to curb terrorism worldwide. Republicans and Democrats alike, in both the House and the Senate, also urged caution, saying that Congress and the public still do not have all the facts and should not prejudge the outcome of the military investigations. "While it's too early to pass judgment on what happened, things don't look good," said Sen. James Inhofe, a conservative Republican. Added Sen. Ben Nelson, one of the more conservative Democrats: "If the initial reports are true, ... clearly, it's an atrocity." "What we do know is pretty ugly stuff," said Republican Rep. Adam Putnam, who returned from Iraq days ago. "I fear that Haditha can have even greater negative consequences in perception than Abu Ghraib," the prison where US soldiers abused Iraqi prisoners in 2004. Rep. C.A. "Dutch" Ruppersberger, a Democrat, who also recently returned from Iraq, said that if substantiated, what happened at Haditha "hurts our reputation in the world."