A tough-talking U.S. President George W. Bush said again Wednesday there is no room to negotiate on approving a bill that sets a deadline for U.S. forces to withdraw from Iraq.

Citing what he called progress in the Baghdad security plan and reconstruction efforts, Bush told the National Cattlemen's Beef Association in Washington he would not back down on his stance against a Senate bill that would bring home American troops in spring 2008.

The Democrats insist Bush will have to accept some sort of troop withdrawal deadline in exchange for the billions of dollars needed to fund the war.

But Bush promised he would shoot down any funding legislation that involves such a timetable, which he considers "meddling" in wartime strategy.

"The House and Senate bill have too much pork, too much restriction on commanders for an artificial [troop] withdrawal," he said. "I've made it clear for weeks if either version of these bills [from the House or the Senate] come to my desk, I will veto it."

In a warning to Democrats, he also said the Democrat-controlled Congress would have to answer to the public for any delays in funding military operations.

"If Congress fails to pass a bill to fund our troops on the front lines, the American people will know who to hold responsible," he said, noting money for U.S. operations in Iraq and Afghanistan begins running out in mid-April and "the clock is ticking."

Bush again invoked the Sept. 11, 2001, terrorist attacks as a reason why the U.S. must see the war through until Iraq's democracy can stand on its own.

"The lesson of Sept. 11 must not be forgot. To cut off support for the security forces would put our own security at risk," he said.

During debate on war funding on Tuesday, the Senate voted 50-48 in favour of upholding a timeline proposal in a war spending bill. The Senate resumes debate on the bill Wednesday.

Senate Majority Leader Harry Reid said he hoped the president understands "how serious we are."

With files from the Associated Press