US President Donald Trump says he plans to sign an executive order ending the constitutional right to citizenship for babies born to illegal migrants in the United States.

The President’s comments to news program Axios on HBO late Tuesday (AEST) come amid a renewed push for hardline immigration policies ahead of the US mid-term elections, and as thousands would-be migrants in the so-called migrant caravan approach the US border with Mexico..

Mr Trump believes focusing on immigration will energise his supporters and help Republicans keep control of Congress.

Revoking birthright citizenship would spark a court fight over the President’s ability to unilaterally change an amendment to the US Constitution. Many scholars speaking to US media say he does not.

The 14th Amendment guarantees the right of citizenship for all children born in the US.

Mr Trump has long called for an end to birthright citizenship, as have many conservatives.

Asked about the legality of such an executive order, Mr Trump said: “They’re saying I can do it just with an executive order”.

“We’re the only country in the world where a person comes in and has a baby, and the baby is essentially a citizen of the United States,” he added.

A 2010 study from the Centre for Immigration Studies showed that 30 countries offered birthright citizenship.

Mr Trump said White House lawyers are reviewing his proposal. It is unclear how quickly he’d act on his plans.

The citizenship proposal comes after US military announced Tuesday more than 5200 troops, including armed soldiers, will be deployed to bolster MrTrump’s efforts to secure the border with Mexico.

General Terrence O’Shaughnessy, the head of US Northern Command, said 800 US troops were already on their way to the Texas border and 5200 would be headed to the south-west region by week’s end, far higher than the 800 to 1000 initially forecast.

-with AAP