US President Donald Trump discusses Tehran nuke pact with Theresa May

US President Donald Trump spoke with British Prime Minister Theresa May and discussed issues including the Iran nuclear deal and the promotion of free and fair trade in particularly with regard to China.

In the call with May on Saturday, Trump also talked about denuclearisation of the Korean Peninsula, the White House said. President Trump "underscored his commitment to ensure that Iran never acquires a nuclear weapon," it said.

Trump's remarks came ahead of British Foreign Secretary Boris Johnson's visit to Washington to urge him not to scrap the Iranian nuclear deal.

The UK and its European allies have until May 12 to persuade Trump to stick with the deal.

President Trump has frequently criticised the Obama-era Iran nuclear deal, also known as the Joint Comprehensive Plan of Action or JCPOA.

Trump has set a May 12 deadline for the US and Europe to address the issues he has with the nuclear deal — under US law, the President has to recertify the deal every few months.

The Iran nuclear deal was reached in Vienna in July 2015 between Iran and the P5 (the five permanent members of the UN Security Council) plus Germany and the European Union.

"The two leaders discussed the promotion of fair and reciprocal trade, particularly with regard to China," the White House said.

As planning continues for his upcoming meeting with North Korean leader Kim Jong Un, Trump emphasised his goal of a denuclearised North Korea, it said.

Trump would visit the United Kingdom in July.