Prime Minister Theresa May and US President Donald Trump have discussed the Iran nuclear deal and North Korea in a phone conversation.
Mrs May made clear her thoughts on the impact of America pulling out of the deal and said the UK remains "firmly committed" to the international agreement that Mr Trump has condemned.
The two leaders agreed for their teams to hold discussions on the potential impact of US sanctions on firms doing business in Iran, Downing Street said.
The telephone call covered other international issues with Mrs May congratulating the US president on the safe return of three Americans who had been held in prison in North Korea.
A spokesman for Mrs May said: "The Prime Minister reiterated the Government's position on the Iran nuclear deal, noting that we and our European partners remain firmly committed to ensuring the deal is upheld, as the best way of preventing Iran from developing a nuclear weapon.
"The Prime Minister raised the potential impact of US sanctions on those firms which are currently conducting business in Iran. They agreed for talks to take place between our teams."
Mr Trump said this week that the 2015 nuclear deal which allowed for the lifting of sanctions was not tough enough on Iran.
The Downing Street spokesman said: "The two leaders looked forward to the summit which will take place between President Trump and Kim Jong-un in Singapore.
"The PM said the UK would continue to work with the US to keep up the pressure on North Korea to denuclearise.
"The Prime Minister and the president condemned the Iranian rocket attacks against Israeli forces earlier this week, and strongly supported Israel's right to defend itself against Iranian aggression.
"They agreed on the need for calm on all sides and on the importance of tackling Iran's destabilising activity in the region."
The two leaders also looked forward to Mr Trump's visit to the UK in July, Downing Street said.