Donald Trump wants to end the constitutional right to citizenship for babies of non-citizens and illegal immigrants born in the US.
The president says he has discussed ending birthright citizenship with White House officials and has been told a constitutional amendment is not necessary.
In an interview with Axios on HBO, Mr Trump said: “It was always told to me that you needed a constitutional amendment. Guess what? You don’t.
“You can definitely do it with an Act of Congress. But now they’re saying I can do it just with an executive order.”
He said he plans to proceed with the new policy by executive order.
Mr Trump said America was the only country in the world to give birthright citizenship, although 30 other countries do so.
He said: “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 for 85 years with all those benefits.
“It’s ridiculous. And it has to end.”
Revoking birthright citizenship would trigger a legal battle over whether the president has the unilateral power to change an amendment to the Constitution.
The 14th Amendment guarantees that right for all children born in the US.
The first line of the 14th Amendment states: “All persons born or naturalised in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.”
Vice President Mike Pence said on Tuesday that Mr Trump revoking birthright may not conflict with the US Constitution.
He said: “The Supreme Court of the United States has never ruled on whether or not the language of the 14th amendment, subject to the jurisdiction thereof, applies specifically to people who are in the country illegally.”
But US House Speaker Paul Ryan was quoted by the Washington Post as saying: “You cannot end birthright citizenship with an executive order”.
The president’s comments come as he takes a tough stance on immigration which he sees as a major battle line in the 6 November midterm elections.
He has vented his fury over a caravan of Central American migrants making its way to the US-Mexico border and is dispatching an additional 5,200 troops to bolster security.
The president said White House lawyers are reviewing his proposal on revoking birthright although it is not clear how quickly he would act on an executive order.
The president has previously described birthright citizenship as a “magnet” for illegal immigration and the 14th Amendment as “questionable” in this context.
One of Mr Trump’s political targets, Democrat gubernatorial candidate Andrew Gillum, responded to the president calling him a “thief” in an interview.
He tweeted: “I heard @realDonaldTrump ran home to @FoxNews to lie about me. But as my grandmother told me – never wrestle with a pig. You both get dirty, but the pig likes it. So ignore him and vote, Florida!”
Florida is a key state in presidential elections and then-governor Jeb Bush oversaw the state-wide count that, after much legal wrangling, decided the 2000 contest in his brother George’s favour.
After Mr Trump responded by suggesting Mr Gillum’s education was limited, the African American mayor of Tallahassee responded by reminding him he had been to a local university.
Mr Gillum faces pro-Trump Republican Ron DeSantis in the 6 November ballot.