The EU's diplomatic chief said Thursday that the bloc would support talks between the U.S. and Tehran, but only if the current nuclear deal with Iran is preserved.

Tehran and Washington have been locked in a bitter standoff since last year when U.S. President Donald Trump unilaterally pulled out of the 2015 deal that gave Iran relief from sanctions in return for curbs on its atomic program.

The idea of direct talks between Washington and Tehran as a way out of the crisis has grown this week after Trump mooted the idea and the new U.S. defense secretary urged Iran's leaders to engage.

The EU has desperately sought to stop the deal from collapsing completely, arguing it is the best way to stop Iran developing nuclear bombs.

EU diplomatic chief Federica Mogherini gave a cautious welcome to the idea of negotiations, after Trump said Monday he was ready to meet Iran's President Hassan Rouhani within weeks.

"We are always in favor of talks, the more people talk, the more people understand each other the better, on the basis of clarity and on the basis of respect," Mogherini said as she arrived for a meeting of EU foreign and defense ministers in Helsinki.

But she added "first and foremost what is existing needs to be preserved" – specifically the 2015 deal known formally as the Joint Comprehensive Plan of Action or JCPOA.