AMES (Iowa) Feb 11: US Senator Barack Obama piled pressure on 2008 White House rival Hillary Clinton over her stand on Iraq on Sunday, questioning how she would live up to her vow to end the war.

Differences between the Democratic heavyweights burst into the open over the conflict, a day after the 45-year-old, who wants to become America's first black president, officially launched his campaign.

“I am not clear on how she would proceed at this point to wind down the war in a specific way,” Obama told reporters when asked to critique Clinton's plans for ending the bloody US engagement during a campaign stop in Iowa.

“I know she has stated that she thinks the war should end by the start of the (next) president's first term, .... beyond that though, how she wants to accomplish that I am not clear, I would let her address those issues,” Obama said.

Obama has put forward a plan to get US combat troops out of Iraq by March 31, 2008.

Clinton wants to cap troop levels in the war-torn nation and opposes President George W. Bush's last ditch surge of forces designed to pacify Iraq.

She has also threatened to work to cut off funds for the Iraqi army, unless Iraqi leaders take responsibility for quelling violence.

“Knowing what we know now, I would never have voted for it,” Clinton said, accusing Bush of misleading the Congress and Americans over the now discredited threat from Saddam Hussein's supposed weapons of mass destruction.

The issue of Iraq is especially problematic for Clinton, as she must woo core Democratic activists who are broadly anti-war to win the 2008 Democratic Party nomination.

Obama tells every audience he meets that he is proud that he was against the war from the start, and thought its implications could be difficult to predict.

He did not face the intense political pressure to vote in favour of the war like Clinton, as he was a state legislator at the time.

“We ended up authorising a war that should never have been authorised and never been waged ... (we've) seen over 3,000 lives of the bravest young Americans wasted ... 25,000 amputees,” Obama told cheering Democratic activists in a rally in Ames, Iowa on Sunday.—AFP