US President Donald Trump pushed British Prime Minister Theresa May to harden her Brexit negotiations with the European Union during an interview broadcast on ITV on Sunday.

"Would it be the way I negotiate? No, I wouldn't negotiate it the way it's (being) negotiated ... I would have had a different attitude," he told Piers Morgan.

"I would have said that the EU is not cracked up to be what it's supposed to be. And I would have taken a tougher stand in getting out."

The UK is set to leave the bloc in March 2019, but with trade negotiations starting this year, May's Conservative Party and her Cabinet are deeply divided over how Brexit should go ahead.

A rock and a hard place

May is under pressure from both wings of her ruling Conservative party to offer greater clarity in public about what Brexitdeal she wants. Senior conservatives are reportedly warning she could be ousted if she fails to define her position soon.

Brexit legislation will get its first debate in parliament's upper chamber this week, with peers from all sides reportedly considering rewriting the EU Withdrawal Bill.

May is also facing demands to sack her finance minister, Philip Hammond, after his recent call for a "very modest" Brexit. So-called "soft Brexiteers," including Hammond, are pushing for the UK to stay in the customs union with the EU.

On the "hard Brexit" side, the European Research Group consisting of about 60 pro-Leave Conservative deputies has said staying in the customs union would make the UK "a vassal state" of the EU during the transition period. This, they argue, would mean that the UK was unable to negotiate trade deals with new partners, but would also have no say in defining trade policy in Brussels.

Come trade with me

In this context, Trump's offer of a post-Brexit trade deal with London that, he said, would be "very swift," appears to represent an incentive to harden May's line in talks with Brussels.

"We are going to make a deal with (the) UK that'll be great," he said, noting constraints imposed by the Brexit process. "When that restriction is up we're going to be your great trading partner."

Trump meanwhile attacked EU trade policy, saying, "We cannot get our product in. It's very, very tough. And yet, they send their product to us — no taxes, very little taxes ... [These problems] may morph into something very big" [from a trade standpoint]," he said.

"They're not the only one, by the way, and I could name many countries and places that do (the same). But the European Union has been very, very unfair to the United States. And I think it will turn out to be very much to their detriment."

Paris climate accord

Trump also appeared open to revisiting his plan to withdraw from the 2015 Paris climate accord if the deal could be substantially revised.

"If somebody said, go back into the Paris accord, it would have to be a completely different deal because we had a horrible deal," Trump said.

"Would I go back in? Yeah, I'd go back in. I like, as you know, I like Emmanuel (Macron). I would love to, but it's got to be a good deal for the US."

jbh/aw (AP, AFP)