Britain warned on Wednesday that it would trigger a return of UN sanctions on Iran, if needed, to prevent it from getting a nuclear weapon as the Security Council met to discuss Tehran's expansion of its stock of uranium close to weapons grade.
Iran has denied wanting to develop a nuclear weapon.
However, it is "dramatically" accelerating enrichment of uranium to up to 60% purity, close to the roughly 90% weapons-grade level, the UN nuclear watchdog - the International Atomic Energy Agency - has warned.
Western states say there is no need to enrich uranium to such a high level under any civilian program and that no other country has done so without producing nuclear bombs. Iran says its nuclear program is peaceful.
"We are clear that we will take any diplomatic measures to prevent Iran acquiring a nuclear weapon, that includes the use of snapback (of sanctions), if needed," Britain's deputy UN Ambassador James Kariuki told reporters ahead of the meeting.