WASHINGTON (WASHINGTON POST) - The White House has signalled to congressional Republicans that it will not shut down the government in October if money isn't appropriated to build a wall along the Mexico border, potentially clearing a path for lawmakers to reach a short-term budget deal.

Congress has only appropriated money to fund government operations through to the end of September, and President Donald Trump has threatened to shut down the government if they don't include US$1.6 billion (S$2.1 billion) in new funding so that 119 new kilometres of wall and secondary fencing can be added to the border.

"Build that wall," Trump said at the Aug 22 rally in Phoenix.

"Now the obstructionist Democrats would like us not to do it. But believe me, if we have to close down our government, we're building that wall."

But shortly after Trump made those comments, White House officials quietly notified Congress that the US$1.6 billion would not need to be in a "continuing resolution" that was meant to fund government operations from October until sometime in early December, a senior GOP congressional aide said.

White House officials have signalled to lawmakers, however, that the wall's eventual construction remains a top priority for Trump. He wants this funding to be included in the December budget Bill, GOP congressional aides said.

Trump could still follow through on a threat to shut down the government in December, but this marks the second time he has pulled back from the wall demand in order to allow lawmakers to pass a budget Bill.

The first time came in May, when lawmakers voted to authorise government funding through September and refrained from including money that would allow for the construction of a new wall. That law, however, did allow the US government to replace existing border wall with a new barrier where necessary.

Trump has been threatening to shut down the government for months.

In May, he said in another tweet that the government needed a "good shutdown" to break the gridlock in Congress.

Because government funding will expire on Sept 30, congressional leaders plan to introduce a Bill that would essentially finance government operations at existing levels into some time in December. Such a Bill would require support from Democrats in the Senate in order to pass, and many Democrats oppose construction of the border wall.

That's one reason many Republicans in Congress have told Trump to focus on other parts of his agenda and postpone having a fight about constructing the border wall for now.

If Trump decided to veto a funding Bill passed by Congress, it would lead to a partial government shutdown. National parks would close, and many government agencies would send employees home without pay, causing delays at Social Security, the Internal Revenue Service and at numerous other agencies.

The last time there was a government shutdown was in 2013.

Building a wall along the Mexico border was one of Trump's biggest promises during his campaign, often thrilling his supporters at rallies with chants of "Build That Wall."

A key part of the promise, however, was that Mexico would pay for the wall's construction.

Mexican officials have refused to play any part of paying for the wall, leading Trump to insist that the money first come from the US Congress so that construction can begin.