US PRESIDENT DONALD Trump has issued an executive order for a wall to be built on the Mexican border.

He also signed measures targeting US “sanctuary” cities, where local officials refuse to help round up people for deportation. He has signed an action to strip funds from the cities.

Speaking to ABC today, Trump promised “100%” to make Mexico pay for the wall, something that the Mexican government has repeatedly said it will not do.

“Ultimately it will come out of what’s happening with Mexico, we’re going to be starting those negotiations relatively soon. And we will be, in a form, reimbursed by Mexico.

All it is, is we will be reimbursed at a later date from whatever transaction we’ll make from Mexico.”

“I’m just telling you, there will be a payment, it will be in a form, perhaps a complicated form.

What I’m doing is good for the United States, it’s also going to be good for Mexico. We want to have a very stable, very solid Mexico.

AFP reports that much of the land needed to build the wall is privately owned, implying lengthy legal proceedings, political blowback, and substantial expropriation payments.

Some of the border is already fenced, but Trump says a wall is needed to stop illegal immigrants entering from Latin America.

In 2014, there were an estimated 5.8 million unauthorised Mexican migrants in the United States, according to Pew, with fewer arriving each year.

Experts have voiced doubts about whether a wall would actually stem illegal immigration, or if it is worth the billions it would be expected to cost.

But the policy has become a clarion call for the US right and far-right – the core of Trump’s support.

Additional reporting by AFP.