LONDON (REUTERS) - Britain, France and Germany have agreed that the nuclear deal that US President Donald Trump has threatened to scrap remains the best way of stopping Tehran getting nuclear weapons, British Prime Minister Theresa May's office said on Sunday (April 29).

May had phone calls with French President Emmanuel Macron and German Chancellor Angela Merkel where they agreed the deal may need to be broadened to cover areas such as ballistic missiles, what happens when the deal expires, and what they consider Iran's destabilising regional activity, a statement said.

"They committed to continue working closely together and with the US on how to tackle the range of challenges that Iran poses - including those issues that a new deal might cover,"the statement said.

This comes as a deadline looms next month for Trump to decide on whether to restore US economic sanctions on Tehran - something which could destroy the 2015 agreement which lifted some sanctions in exchange for curbs on Iran's nuclear programme.

Speaking on a whistle-stop Middle East tour on Sunday, Secretary of State Mike Pompeo said Washington would abandon the nuclear deal unless talks with European partners yield improvements.

"We've certainly made some (progress with the Europeans),"he said. "There is still work to do. They said: 'Great, we will support you if you get the fixes'."

Macron later spoke with President Hassan Rouhani and agreed to work with him in coming weeks to preserve the nuclear deal, his office said in a statement.

The French president also called for discussions on Iran's ballistic missile programmes, its nuclear activities beyond 2025 and the country's role in Middle East crises, according to his office, in a conversation that lasted more than an hour.