US Secretary of State John Kerry, EU foreign policy chief Catherine Ashton and Irans Foreign Minister Javad Zarif are in Muscat on 9 and 10 November to continue negotiations over Irans nuclear programme.
The differences to be resolved include the Islamic Republics compliance with International Atomic Energy Agency (IAEA) monitoring, the extent to which it could continue its peaceful nuclear programme and the timetable for lifting sanctions.
These serious points of contention reduce the likelihood of a deal being reached before the final 24 November deadline.
Another round of negotiations will begin in Vienna on 18 November, with a full Iranian delegation and representatives of the P5+1 powers China, France, Russia, the UK, the US and Germany.
Iran is keen to reach an agreement as Western sanctions are severely affecting its economy and exports. Deputy Foreign Minister Abbas Araqchi remained positive, and was reported as saying all sides are very optimistic on clinching a deal by the Islamic Republic News Agency.
However, the US Department of State continued to cite concerns over monitoring and verification.
An agreement on the nuclear programme would result in sanctions being gradually lifted, widening the opportunities for foreign investment in the regions third-largest market. Iran has historically been an important trading partner for the UAE, Oman, Qatar and Kuwait, but this trade has suffered due to political tensions since 2012.
The end of the long stand-off between the US and Iran could also facilitate cooperation in combating the jihadist group Islamic State in Iraq and Syria (Isis), although the US denies this possibility.