World powers are set to resume talks in Vienna on Friday in an effort to bring the United States and Iran to compliance with a nuclear deal that has been unraveling ever since the US removed itself three years ago.

Both US and Iran representatives spoke favorably of the ongoing mediation that kicked off on Tuesday, despite neither side meeting in person.

Delegates from the remaining signatories to the treaty — China, Russia, France, Germany, and the United Kingdom — met separately on Wednesday with Iranian and US representatives in a bid to sound out their position.

The five nations have agreed to set up two expert groups to try to align the sanctions that the US is ready to lift with curbs that Iran could allow to reimpose on its nuclear program. The experts will brief the Joint Commission of the Joint Comprehensive Plan of Action on their progress.