Britain once again told Iran on Sunday that this is the last chance for its negotiators to present serious proposals and save the 2015 nuclear deal, the JCPOA.

"This is the last chance for Iran to come to the negotiating table with a serious resolution to this issue, which has to be agreeing the terms of the JCPOA," British Foreign Secretary Liz Truss said.

"This is their last chance, and it is vital that they do so. We will not allow Iran to acquire a nuclear weapon."

Truss had sent the same message to Tehran on December 8, saying “This is really the last chance for Iran to sign up and I strongly urge them to do that because we are determined to work with our allies to prevent Iran securing nuclear weapons," she told the Chatham House think tank.

Negotiation to revive the JCPOA resumed Thursday amid pessimism over Iran’s readiness to embrace understandings reached in earlier talks this year. The new hardliner government in Tehran has adopted a tougher position since after a 5-month interruption the talks reconvened on November 29.

Germany's foreign minister warned Saturday that time was running out to revive the nuclear deal. She was speaking after meetings with her G7 counterparts.