The coming weeks are decisive for the future of the nuclear deal with Iran, German Chancellor Angela Merkel said on Sunday.
The German leader added that every day that passes without Tehran responding to US overtures will result in Iran enriching more uranium.
Speaking during a visit to Israel, the outgoing chancellor said that Russian President Vladimir Putin and Chinese President Xi Jinping also had a responsibility to help to push Iran back to the negotiating table, she said at a joint news conference with Israeli Prime Minister Naftali Bennett.
Western powers have been warning that time is running out to save the 2015 nuclear deal (JCPOA) but so far have taken no action.
"I also see a responsibility for Russia and China here, since if the JCPOA (nuclear deal) is no longer doing what it's meant to do then that's very difficult, so we are now in very decisive weeks for this deal."
Iran in June suspended nuclear negotiations that had started in Vienna in April, saying its new government needed time to prepare for further talks, but so far has delayed a decision.
Iran's nuclear chief Mohammad Salami told state television on Saturday that Tehran has stockpiled 120 kg of 20-percent enriched uranium.
With reporting by Reuters