US undersecretary for international trade David Aaron told reporters approval of a full $18 billion funding package by Congress, where it is held up by political wrangling, was crucial to containing world financial turmoil.

"It would be not responsible for Congress to fail to come forward to support this," said Aaron, who is leading a high-level trade mission to Asia.

"This is no time to be under-funding the lender of last resort in the international financial world. The world is gripped with an economic crisis and we are at a very, very delicate stage," he said.

An $18 billion funding package requested by the White House to replenish the IMF's dwindling coffers has been approved by the US Senate but is tied up in the Republican-dominated lower house.

After multi-billion dollarbailouts of Russia and several Asian economies in the past year the IMF is in urgent need of fresh funds to help contain spreading financial crisis.

A Republican-led appropriations committee has approved $3.4 billion in funds, a fraction of the $18 billion the administration says is required and has requested.

Aaron said he thought Congress would eventually come through with approval for the full package but there would be no easing of pressure until then.

"We are going to continue to press. The president made it very clear in his speech on Tuesday, we are going to continue to press Congress for the fourteen and a half (billion) additional subscription. We think it's crucial," he said.

"I have some confidence that they will, but the time for action is now," he said.

Senior US policy makers, including treasury secretary Robert Rubin and Federal Reserve chairman Alan Greenspan have also urged the approval of the full funding package.