The trip to Egypt and Israel, due to begin Tuesday, has been pushed back to mid-January, allowing Pence to remain in Washington in case he needs to cast the deciding vote in the Senate over President Donald Trump's tax reforms.

"The tax vote is still in very good shape, but we don't want to take any chances whatsoever," said a senior administration official.

Senator John McCain's return home to Arizona to fight cancer has left Republicans with a razor-thin margin to push the legislation over the finishing line.

Having failed to clear a series of legislative hurdles, the package is seen as key to Trump's ability to secure support among his base and skittish political donors.

"We have some senators who obviously can't make it there for the vote and the vice president feels that it's important for him to be here for the largest tax cut in history," the official said.

The House of Representatives is expected to vote on the package on Tuesday with the Senate vote to follow late Tuesday or early Wednesday.

Officials denied that Pence's decision was motivated by a wave of deadly protests in the wake of Trump's controversial decision to declare Jerusalem as Israel's capital.

"This is all about the largest tax cut in American history and having the vice president and the full team here," the official said.

"It's an odd case to make given we are going to be there in two or three weeks," a second senior White House official said, slapping down suggestions of a delay.

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