Republicans in the US Senate have blocked a Democratic proposal to tie a $50bn (£24bn) Iraq war funding bill to a timetable for troop withdrawal.

The 53-45 vote was not enough to advance the bill, which passed in the House of Representatives on Wednesday.

President George W Bush has asked Congress for extra emergency funding for operations in Iraq and Afghanistan.

Defense Secretary Robert Gates warned that if the money was not approved, funds would run out by February.

In a sign of the tussle over the issue in the closely divided chamber, Democrats had earlier blocked a Republican proposal to give Mr Bush $70bn in funds without attaching a timetable for withdrawal.

The Bush administration wants Congress to pass the additional war funds as soon as possible but without conditions attached.

Democratic-led attempts to attach conditions to war funding have repeatedly failed because the party has not been able to muster the two-thirds majority to override a presidential veto.

But the Democrats continue to insist that they will not approve more funding unless Mr Bush agrees to conditions including a timetable for troop withdrawal.

"Our troops continue to fight and die valiantly. And our Treasury continues to be depleted rapidly for a peace that we seem far more interested in achieving than Iraq's own political leaders," Senate Majority Leader Harry Reid said.

Friday's vote means that a bill is unlikely to be sent to President Bush until January at the earliest.

The Republicans accused the Democrats of irresponsibility.

"We need to get our troops everything they need. We need to get it to them right now," said Senate Republican Leader Mitch McConnell.

White House spokesman Tony Fratto said that the Pentagon would have to start using its annual budget to cover costs.

"We'd rather see the department of defense, the military planners and our troops focusing on military maneuvers rather than accounting maneuvers as they carry out their mission in the field," he said.

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Defense Secretary Robert Gates