Negotiators from Iran and the remaining parties to the agreement _ Britain, France, Germany, Russia and China _ are working in Vienna to restore life to the accord, which granted Iran sanctions relief in exchange for curbs on its nuclear program.

The United States has participated indirectly in the talks because it withdrew from the deal in 2018 under then-President Donald Trump. President Joe Biden has signaled that he wants to rejoin the deal.

Under Trump, the U.S. reimposed heavy sanctions on Iran. Tehran has responded by increasing the purity and amounts of uranium it enriches and stockpiles, in breach of the accord _ formally known as the Joint Comprehensive Plan of Action, or JCPOA.

Scholz told participants at the annual Munich Security Conference on Saturday that talks have come a long way over the past 10 months and ``all elements for a conclusion of the negotiations are on the table.''

But he also criticized Iran for stepping up its enrichment and restricting inspections by monitors from the UN nuclear agency.

``We now have the opportunity to reach an agreement that makes it possible for sanctions to be lifted,`` Scholz said. ``At the same time, it's the case that if we don't succeed very quickly in this, the negotiations threaten to fail.''

``The Iranian leadership now has a choice,`` the chancellor said. ``Now is the moment of truth.''