US Republican presidential candidate Donald Trump has insisted Mexico will pay for a border wall "100%", in a major immigration speech.

He told a cheering crowd in Arizona that he would secure the border, and left open the possibility that millions of illegal immigrants be deported.

Hours earlier, he met Mexican President Enrique Pena Nieto but said they had not discussed financing the wall.

The president later insisted he had told Mr Trump Mexico would not pay.

There had been speculation that the Republican candidate would back off his plan to deport the estimated 11m undocumented immigrants living in the US.

In his speech in Phoenix, there were conflicting signals about this. He said their fate was not a "core issue" and that deporting "criminal aliens" would be the priority.

"We will treat everyone living or residing in our country with great dignity," he said.

But later he struck a more uncompromising note when he added: "Anyone who has entered the United States illegally is subject to deportation. That is what it means to have laws."