Donald Trump, who once claimed that healthcare reform would be "easy", has now likened it to the Middle East peace process.

Trump was speaking to reporters aboard Air Force One while travelling to France to mark Bastille Day with the Emmanuel Macron when he said: "I'd say the only thing more difficult than peace between Israel and the Palestinians is healthcare."

It comes amid fierce debate in Washington as senators attempt to find a replacement to Obamacare.

Republican leaders are struggling to get enough support to pass a bill that could replace the Affordable Care Act.

Some senators are nervous that changes could negatively impact them ahead of 2018 mid-term elections.

Speaking about the need to get the votes to pass the bill, Trump said: "It's like this narrow road that's about a quarter of an inch wide.

"You get a couple here and you say, great, and then you find out you just lost four over here. Healthcare is tough."

It was a rare opportunity for reporters to speak to the president, who has shied away from conferences and questions since his election victory.

He spoke for almost an hour in what was initially an off-the-record meeting, but Trump later allowed journalists to report on his comments.

Before attending the Bastille Day military parade, Trump issued a series of tweets aimed at Republicans to push them into reaching an agreement.

He tweeted: "Republicans Senators are working hard to get their failed ObamaCare replacement approved. I will be at my desk, pen in hand!

"So impt [important] Rep Senators, under leadership of @SenateMajLdr McConnell get healthcare plan approved. After 7yrs of O'Care disaster, must happen!

"After all of these years of suffering thru ObamaCare, Republican Senators must come through as they have promised!

"Mike Pence is working hard on HealthCare and getting our wonderful Republican Senators to do what is right for the people."