Donald Trump remained resolute in his demand for funding for a border wall on Sunday as negotiations between Democrats and Republicans, to strike a deal and reopen the US government, stalled.

Apparently content to let the shutdown continue indefinitely, he left for meetings at Camp David as determined as ever to secure the $5.6 billion requested to finance his key campaign pledge.

In Washington Mike Pence, the vice president, restarted talks with key Democrat representatives in an attempt to break the deadlock with the looming threat that Mr Trump may invoke emergency powers in order to get the wall built.

Meanwhile, Mick Mulvaney, his acting chief of staff, said the US president was prepared to take the notion of a concrete wall permanently "off the table" replacing it with a "steel fence" as a concession to Democrats.

Moments before boarding Marine One, the presidential helicopter, Mr Trump said: "We have to build the wall or we have to build a barrier.

"It (the shutdown) is a very important battle to win. This wall will pay for itself many times over the course of this year. Most importantly it's about safety. It's not just illegals. It's criminals, it's drugs, it's human trafficking, where they grab women and sell them."