A leading US Republican senator has said the war in Iraq is looking more like the Vietnam conflict from a generation ago.

On Sunday, Nebraska Senator Chuck Hagel, who received two Purple Hearts and other military honours for his service in Vietnam, reaffirmed his position that the US needs to develop a strategy to leave Iraq.

"Stay the course is not a policy," said Hagel, a possible contender in the 2008 presidential election. "By any standard, when you analyse two and a half years in Iraq ... we're not winning."

Hagel said more US troops was also not the solution.

"We're past that stage now because now we are locked into a bogged-down problem not dissimilar to where we were in Vietnam," Hagel said.

"The longer we stay, the more problems we're going to have."

Hagel argued that the similarities were growing.

"What I think the White House does not yet understand - and some of my colleagues - the dam has broke on this policy," Hagel said.

"The longer we stay there, the more similarities [to Vietnam] are going to come together."