MOSCOW (AP) — Iran and six world powers resume nuclear talks Monday no closer to progress than in previous rounds, and with the clock ticking on international diplomatic efforts to persuade Tehran to curb activities that could be used to make atomic arms.

Diplomats from several nations meeting with Iran in Moscow depict the talks as crucial. They say it will likely be the last in a series and that, if negotiators fail to make headway in persuading Tehran to stop higher-grade uranium enrichment, it’s unclear if or when new talks would occur.