After so many years of suspicion and mutual antagonism, it is remarkable how quickly the relationship between Washington and Tehran has changed.

Much of the credit must go to President Hassan Rouhani who, since being elected in June, has led a concerted diplomatic charge to repair Iran’s position in the world. Credit is also due to US and European leaders for showing a willingness to grasp the opportunity.

It is in everyone’s long-term interests for Tehran to play a normal role on the international stage and for its pariah status to be removed. Iranians would benefit from an economy able to trade freely with the region and the world. A reduction in tensions with GCC neighbours should be something Gulf states welcome too. There are many, however, who will be suspicious and Iran’s change of tone will only go so far in placating them. In particular, it will take more than the end of nuclear enrichment to dispel the deeply ingrained notion among Israelis that Tehran would like to see the end of their state.

Arab leaders, who like to cast the region’s political issues in sectarian terms, will also have their doubts. Tehran’s involvement in many of the region’s flashpoints, including Syria, Iraq, Lebanon and the Palestinian Territories, is viewed as pernicious at best in many Gulf capitals. Any sense that Iran might have greater room for manoeuvre without the constraint of international sanctions will make some even more fearful.

Rouhani has been reaching out to the GCC states, meeting Oman’s Sultan Qaboos bin Said al-Said in August and speaking with Qatar’s Emir Sheikh Tamim bin Hamad al-Thani by telephone this month. But others will be harder to convince, particularly Saudi Arabia.

It will be the job of US leaders and diplomats, more than anyone else, to try and assuage those concerns. For the detente process to be a success, it will require a wide-ranging, long-term commitment by the US and other world powers to act as guarantors and policemen.