Getty ImagesSir Keir Starmer and Donald Trump discussed "ongoing and productive" trade talks, No 10 has said, in their first call since the US president imposed tariffs on UK goods.
The prime minister stressed his commitment to "free and open trade and the importance of protecting the national interest", a Downing Street spokesperson said.
They added that the two leaders also discussed "the situation in Ukraine, Iran and recent action taken against the Houthis in Yemen".
Sir Keir is hoping to secure a deal with the US after Trump unveiled 10% tariffs on UK goods and a higher 25% rate on imports of cars, steel and aluminium.
"The leaders began by discussing the ongoing and productive discussions between the UK and US on trade," No 10 said in a statement.
US Vice-President JD Vance said on Tuesday there was a "good chance" a trade deal could be reached with the UK.
Trump announced a barrage of tariffs earlier this month and shares on stock markets around the world have since tumbled.
The S&P 500 index of the largest firms listed in the US, the UK FTSE 100, German Dax, and French Cac 40 have recovered some value as Trump has delayed some tariffs and made exceptions, but are lower than before 2 April.
The current tariff policy now puts a 10% "baseline" tariff on all imports from the UK, France and other long-standing trade partners. China faces much harsher tariffs.
A tariff is a tax on businesses buying a good from overseas, but businesses often pass the costs from the tariff onto the consumer or overseas the seller.
The World Trade Organization said on Wednesday that global trade will shrink as a result of the tariffs while the International Monetary Fund downgraded its predictions for growth because of them.
The UK has been trying to avoid the tariffs by agreeing some kind of economic deal with the US, while the EU and Canada has responded with counter tariffs.
