Trump visited the US-Mexico border in Mission, Texas [Source: Reuters]

US President Donald Trump has threatened again to declare a national emergency to fund a border wall without Congress’s approval.

Trump says he has the absolute right to declare a national emergency,” as he headed to an event at the border.

He says Mexico would “indirectly” pay for the wall – contradicting an earlier campaign memo.

The government has been in partial shutdown for 20 days, leaving about 800,000 federal employees without pay.

President Trump refuses to sign legislation to fund and reopen the government if it does not include $5.7bn for a physical barrier along the US-Mexico border.