Senator Barack Obama piled pressure on Hillary Clinton over Iraq, as his Democratic presidential rival faced mounting scrutiny over her vote to authorise the war in 2002.
Obama questioned on Sunday how the New York Senator would make good on her vow to end what he is calling a "tragic" conflict that should never have been waged, as he fired up packed campaign rallies in Iowa and his hometown of Chicago.
Clinton, on the stump in New Hampshire in the fast moving opening skirmishes of the most open presidential election in 80 years, was meanwhile again taken to task by core Democratic activists over her position on Iraq.
<b1>"I am not clear on how she would proceed at this point to wind down the war in a specific way," Obama, 45, 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, on a quest to become the first African-American US president, has put forward a plan to get US combat troops out of Iraq by March 31, 2008.
Clinton in Nashua, New Hampshire, where Obama will campaign today, was challenged by an identified guest at Democratic party who said her position on Iraq "doesn't fly".
She was also asked whether she should admit that her vote on Iraq was a mistake, as did another one of her rivals, defeated 2004 Democratic vice presidential pick John Edwards.