The United States cannot unilaterally terminate a 2015 nuclear deal between Iran and world powers, Federica Mogherini, the foreign policy chief of the European Union, has said.

Mogherini made the comments on Friday, just minutes after US President Donald Trump announced his decision not to certify the landmark accord.

READ MORE: What you need to know about Trump and the Iran deal

"We cannot afford as the international community to dismantle a nuclear agreement that is working," said Mogherini, who chaired the final stages of the talks in July 2015

"This deal is not a bilateral agreement, this is not an international treaty ... so it is clearly not in the hands of any president of any country in the world to terminate an agreement of this sort," Mogherini told reporters in Brussels.

"The president of the United States has many powers, but not this one," she added.

"The international community, and the European Union with it, has clearly indicated that the deal is, and will, continue to be in place."

Mogherini said she spoke to Rex Tillerson, the US secretary of state, immediately after Trump's speech on Friday.