The US has been appealing to Britain, France and Germany to push for changes to the 2015 agreement, signed by then president Barack Obama and much criticised by his successor Donald Trump.

"I think there is a common view among the E3 that there are some areas of the JCPOA (nuclear deal) or some areas of Iran behaviour that should be addressed," Tillerson said in London, referring to the European signatories.

The three countries have agreed to establish a working group which will meet somewhere in Europe during which Tillerson said he "will see what progress we can make".

Trump has demanded changes be made to the nuclear deal and has threatened to withdraw US support, although earlier this month agreed again to waive nuclear-related sanctions on Iran.

The US is also concerned about Iran's "arms exports to Yemen and elsewhere", Tillerson said, and restrictions on the country that the deal gradually lifts beginning in 2025.

While in London, Tillerson met with his British counterpart Boris Johnson and Prime Minister Theresa May.

"They agreed on the importance of the international community coming together to counter Iran's destabilising regional activity, and the prime minister reiterated the UK's commitment to the Iran nuclear deal," the premier's spokeswoman said after their meeting.

Both Tillerson and Johnson said they would examine Iran's ballistic missile programme, which was not part of the 2015 accord.

According to the British foreign minister, there is a "pretty wide measure of agreement on the European side" to "constrain that activity".

The ballistic missile programme will be on the agenda when French Foreign Minister Jean-Yves Le Drian visits Iran on March 5, when he will also address Tehran's role in regional conflicts.

Iran was also being discussed at a meeting of European Union foreign ministers in Brussels on Monday, ahead of which Le Drian said the group would stay "firm" on the need to preserve the agreement.

The EU is working alongside the European signatories on a response to Trump's 120-day deadline for US lawmakers and European allies to fix "disastrous flaws" in the deal or face a US exit.