U.S. Defence Secretary Donald Rumsfeld said he never glossed over the difficulties of the fighting in Iraq.

Hillary Rodham Clinton called on Donald Rumsfeld to resign on Thursday, hours after excoriating the defence secretary at a public hearing over what she called the "failed policy" in Iraq.

"Under your leadership, there have been numerous errors in judgment that have led us to where we are," the Democratic senator from New York told Rumsfeld during a hearing before the Senate armed services committee. "We have a full-fledged insurgency and full-blown sectarian conflict in Iraq."

The defence secretary rejected some of her specific criticisms as simply wrong and said the war against terror will be a drawn-out process. He said he never glossed over the difficulties of the fighting.

"I have never painted a rosy picture," he said. "I've been very measured in my words, and you'd have a dickens of a time trying to find instances where I've been excessively optimistic."

She later told the Associated Press that President George W. Bush should accept Rumsfeld's resignation.

Credibility 'lost'

"The secretary has lost credibility with the Congress and with the people," she said. "It's time for him to step down and be replaced by someone who can develop an effective strategy and communicate it effectively to the American people and to the world."

Asked about Clinton's comments, Pentagon spokesman Eric Ruff said: "We don't discuss politics."

Clintonhad resisted joining the Democratic chorus demanding Rumsfeld's ouster. Her remarks Thursday were the harshest assessment yet from the woman consideredthe early front-runner for the 2008 Democratic presidential nomination.

The former first lady has come under attack from some in her own party for voting for the war in 2002 and her current opposition to a deadline for U.S. troop withdrawal.

Pentagon chiefs warn of possible civil war

Two top Pentagon commanders told the committee that spiraling violence in Baghdad could propel Iraq into outright civil war, using a politically loaded term that the Bush administration has long avoided.

The generals said they believe a full-scale civil war is unlikely. Even so, their comments to Congress cast the war in more sombre hues than the administration usually uses, and further dampened lawmakers' hopes that troops would begin returning home in substantial numbers from the widely unpopular war in time for midterm elections this fall.

"I believe that the sectarian violence is probably as bad as I have seen it, in Baghdad in particular, and that if not stopped it is possible that Iraq could move toward civil war," said Gen. John Abizaid, the top U.S. commander in the Middle East.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, told the senators: "We do have the possibility of that devolving into civil war."

There are currently about 133,000 U.S. forces in Iraq. The Pentagon has recently decided to extend the deployment of some 3,500 troops, sending them into Baghdad along with Iraqi forces to bolster security.

U.S. soldiers charged

In another development, assault charges were filed Thursday against three Marines stemming from an incident in April in the Iraqi village of Hamdania, military officials said.

The alleged assault was uncovered during an investigation that previously led to murder charges against seven Marines and a Navy corpsman accused of killing an Iraqi civilian on April 26.

The three charged in the April 10 assault have been identified as Lance Cpl. Saul H. Lopezromo, Pfc. Derek I. Lewis and Lance Cpl. Henry D. Lever. The nature of the assault was not described.

A fourth Marine, an officer, is expected to be charged next week in connection with the assault, said Lt. Col. Colby Vokey, the Marine Corps' defence co-ordinator for the western United States.

The three Marines were charged after the Naval Criminal Investigative Service investigated the April 26 killing of Hashim Ibrahim Awad, 52,in Hamdania.

The eight troops who have been charged with the kidnap and murder of Awad are in the Camp Pendleton brig. A hearing will be held to determine whether there is probable cause for a full trial.