World powers denounce Iran's 'brinksmanship' to enrich uranium to 20%

World powers on Tuesday (July 6) warned Iran that its latest uranium enrichment efforts could imperil the nuclear talks in Vienna, with the United States calling on Tehran to halt its "brinksmanship".

The cross-Atlantic condemnation came hours after the International Atomic Energy Agency (IAEA) reported that Iran intended to enrich uranium to 20%, in the latest sign the talks based in Vienna -- aimed at reviving a 2015 nuclear accord -- could be stalling.

"We continue to urge Iran to stop this brinksmanship, to return to Vienna prepared for real talks, and to be in a position to be prepared to finish the work" that jump-started in April, US State Department spokesman Ned Price told reporters.

Iran's move takes it a step closer to developing materials that could be used to make a nuclear weapon.

"It is worrying that Iran is choosing to continue to escalate its non-performance of its JCPOA [Joint Comprehensive Plan of Action] commitments, especially with experiments that have value for nuclear weapons research," Price said, referring to the nuclear accord that Iran previously agreed to observe.

"It's another unfortunate step backwards for Iran."

European powers also spoke out, with the foreign ministers of Britain, France and Germany expressing "grave concern" and warning that Iran's move endangers the discussions.

Tehran threatens outcome of Vienna talks

"With its latest steps, Iran is threatening a successful outcome to the Vienna talks despite the progress achieved in six rounds of negotiations to date," the ministers said in a statement.

Iran should return to the negotiations "without delay" and aim to bring them to a swift conclusion, they warned. "We have repeatedly stressed that time is on no-one's side."

Britain, France, Germany and the United States are among the global powers, along with China and Russia, that negotiated the deal with Iran aimed at restricting its nuclear programme.

No set timeline on closing the window on negotiations with Iran exists, said Price.

But he made clear that Washington would reconsider if Iran continued with its "provocative steps" aimed at shrinking the breakout time to produce enough fissile material for a bomb -- from a year at the time of the JCPOA to reportedly just months today.

In May, the United Nations nuclear watchdog voiced concern that Iran had not clearly answered queries over possible undeclared nuclear activity, adding that its enriched uranium stockpile was 16 times over the allowed limit.

In April, world powers expressed "grave concern" over Iran's announcement that it would move to boost uranium enrichment up to 60%.