Theresa May and Donald Trump have agreed talks are needed to discuss how US sanctions will affect companies operating in Iran.
Downing Street confirmed the pair talked over the phone and agreed on the importance of destabilising activity in the region.
Mrs May also reiterated her support for the Iran nuclear deal despite Mr Trump's announcement this week that he will pull out of the accord and enforce stronger sanctions on Tehran.
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."
During the phone call, the Prime Minister also congratulated the US President on the safe return of the three US citizens, who were being held in North Korea, and said the UK would keep pressure on Pyongyang to denuclearise.
She then spoke of the need to tackle Iran's "destabilising activity" in the region.
"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," the spokesman added.
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"They agreed on the need for calm on all sides and on the importance of tackling Iran's destabilising activity in the
region."
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