US President Donald Trump has said he will make a major announcement at 20:00 GMT on Saturday about his proposed wall on the United States border with Mexico.

The issue is the core reason behind a bitter dispute between the Republican leader and Democrats, who control the House of Representatives, which has led to a partial government shutdown that has lasted four weeks so far.

"I will be making a major announcement concerning the Humanitarian Crisis on our Southern Border, and the Shutdown, tomorrow afternoon at 3 P.M., live from the @WhiteHouse." Trump wrote on Twitter, late on Friday.

I will be making a major announcement concerning the Humanitarian Crisis on our Southern Border, and the Shutdown, tomorrow afternoon at 3 P.M., live from the @WhiteHouse. — Donald J. Trump (@realDonaldTrump) January 18, 2019

The president wants $5.7bn from Congress to fund the US-Mexico border wall but Democrats have rejected the demand.

800,000 without pay

In response, Trump has refused to approve legislation to restore funding to about a quarter of the federal government, resulting in up to 800,000 employees going without pay.

The House has passed short-term spending bills that would end the shutdown and reopen the government, but Republican Senate Majority Leader Mitch McConnell has refused to allow a floor vote on them, saying they lacked White House support.

During the week, a small group of Senate Republicans sought support for a plan to urge Trump to agree to a short-term funding bill in exchange for a debate on border security. Their efforts went nowhere.

The partial shutdown - already the longest in the US history - seemed certain to drag well into next week, meaning federal workers nationwide would continue to go unpaid and some government functions would remain impaired.

In a sign of just how bitter the dispute has become, Trump denied House speaker, Nancy Pelosi, and a congressional delegation the use of a military plane for a planned visit to Belgium and Afghanistan.