The leaders of France, Britain and Germany warned the United States against taking decisions that could harm the Iran nuclear deal such as re-imposing sanctions after U.S. President Donald Trump's decision not to certify the agreement.

"We encourage the U.S. Administration and Congress to consider the implications to the security of the U.S. and its allies before taking any steps that might undermine the JCPOA, such as re-imposing sanctions on Iran lifted under the agreement," President Emmanuel Macron, Chancellor Angela Merkel and Prime Minister Theresa May said in a joint statement.

Trump struck a blow against the 2015 Iran nuclear agreement on Friday in defiance of other world powers, choosing not to certify that Tehran is complying with the deal and warning he might ultimately terminate it.

The three leaders, who had agreed prior to Trump's announcement to have a common position, stressed that they backed the landmark agreement.

They also said they shared the United States' concerns over Iran's ballistic missile programme and regional activities and were ready to work with Washington to address those concerns.

"We stand ready to take further appropriate measures to address these issues in close cooperation with the U.S. and all relevant partners," they said.

"We look to Iran to engage in constructive dialogue to stop de-stabilising actions and work towards negotiated solutions.