Iran nuclear deal on the line at Tillerson's first meeting with Iran's foreign minister

The US has warned the deal is not working properly and said Washington could withdraw as early as next month.

Rex Tillerson, the US Secretary of State, will sit down at the same table with his Iranian counterpart Mohammad Zarif for the first time on Wednesday at a meeting to review implementation of the 2015 nuclear agreement with Tehran.

The US has warned the deal signed by President Barack Obama, which puts curbs on Iranian nuclear development activity for 15 years, is not working properly and warned Washington could withdraw as early as next month. Mr Trump has to certify that Iran is meeting its end of the deal every three months and the next deadline looms in October.

The New York meeting on the sidelines of the UN general assembly meeting will be closely watched for any signs that Mr Tillerson remains committed to the deal. The gathering will be chaired by Federica Mogherini, the EU foreign policy chief, and include officials from Britain, France, Russia, China and Germany. All six countries conducted years of talks with Iran to conclude the accord two years ago.

State department officials said there were no plans for Mr Tillerson to meet privately with Mr Zarif, a US-educated diplomat who frequently held one-on-one talks with John Kerry, the last secretary of state.

Hassan Rouhani, the Iranian president, warned on Saturday that European nations would play a vital role in protecting the deal. He pointed out that the UN’s nuclear watchdog, the International Atomic Energy Agency had reported Iran was in compliance with the inspections regime.

“[The accord] can serve as a good model for settling the complex international and regional issues,” he said. “We believe that the only entity that can confirm Iran’s commitment to its obligations is the International Atomic Energy Agency and according to its reports, the Islamic Republic has complied with all of its obligations.”

Mr Rouhani is due to arrived in New York for the UN meeting sometime in the next 24 hours. In contrast to recent years he is expected to be on the defensive over the deal.

The New York Times reported last week that the Trump administration was minded to keep the deal but increase the pressure with other sanctions. “We are not going to stand for what they’re doing to this country,” Mr Trump told reporters travelling with him on his plane. “They have violated so many different elements, but they’ve also violated the spirit of that deal. And you will see what we’ll be doing in October. It will be very evident.”

Antonio Guterres, the UN Secretary General, has called for the US to renew its commitment to the deal at the summit.

“It has contributed to an important de-escalation at the moment, and it is a factor of stability," he said. "And it’s my opinion that all parties should do everything possible for this agreement to be preserved.”

The agreement remains the focus of considerable distrust, particularly as Iran’s aggressive foreign policy has fuelled instability around the Middle East. Benjamin Netanyahu, Israel’s prime minister, said an attack on the deal would be at the heart of his address to the UN.

Nikki Haley, America's ambassador to the UN, has described the deal as flawed but added that it may be counterproductive for the US to leave the agreement. “But the deal was constructed in a way that makes leaving it less attractive. It gave Iran what it wanted up front, in exchange for temporary promise to deliver what we want.”

Iranian officials have said it is possible that the US would withdraw from the deal but that Iran would — along with the European and other parties to the deal -agree to continue the nuclear freeze.

Experts believe there is an opportunity for US pressure to achieve concessions from Iran in specific areas, particularly more extensive inspections of state facilities and a revision of the sunset clause that lifts the curbs.