The United States and Israel have warned that they are exploring a “plan B” for dealing with Iran if Tehran does not return in good faith to negotiations to salvage the 2015 nuclear deal.

With talks to revive the deal at a standstill, the US secretary of state, Antony Blinken, said on Wednesday that the window for the Islamic Republic to return to the agreement is closing.

“Time is running short,” he said at a joint press conference with the Israeli foreign minister, Yair Lapid. “We are prepared to turn to other options if Iran doesn’t change course, and these consultations with our allies and partners are part of it.”

“We will look at every option to deal with the challenge posed by Iran,” Blinken said. “And we continue to believe that diplomacy is the most effective way to do that. But, it takes two to engage in diplomacy, and we have not seen from Iran a willingness to do that at this point.”

He did not elaborate, but Lapid, without being contradicted, said of Blinken’s comments: “If a terror regime is going to acquire a nuclear weapon, we must act. We must make clear the civilized world won’t allow it.”

Earlier on Wednesday, the US special envoy, Robert Malley, said that Iran is sending daily signals that it may already have reject a return to talks, requiring the US and European powers to consider all other options.

The US warnings came as the EU chief negotiator Enrique Mora travels to Iran with a message that the talks are in deep crisis, in the latest attempt to convince Tehran to return to talks. A European diplomat said: “It is now up to Iran to unambiguously state its intention and explain its choice to the international community and its own citizens.”

Malley will in the coming days travel to the Middle East to consult on how the US and its allies will respond if it decides it is necessary to break off the talks designed to reinstate the 2015 agreement constraining Iran’s nuclear program.

Iran has so far said it will return “soon” to the talks in Vienna that ended in June when Hassan Rouhani stood down as president, replaced in an election by the hardline Ebrahim Raisi.

The new foreign minister, Hossein Amir-abdollahian, has refused to set a new date for talks to resume, saying Iran needed time to review progress and appoint a new team of negotiators.

US officials believe they cannot wait indefinitely since Iran is developing irreversible nuclear knowledge, taking it closer to the ability to build a nuclear weapon. It has built up a stockpile of highly enriched uranium at 60%, experimented with uranium metal based fuel at 20%, restricted UN nuclear inspections, developed 1,500 advanced centrifuges capable of producing uranium and declared it will use advanced centrifuges at its Fordow site.

Israel, which has not shown a reluctance to bomb Iranian nuclear installations in the past, has been pressing for the US to recognise the new regime in Tehran is ideologically opposed to the nuclear deal known as the JCPOA.

Russia is also urging Iran to return to the talks quickly and not to try to undo the progress made in the first set of talks.

Malley said: “Iran knows that the US is prepared to return to the joint comprehensive plan of action, and quickly lift all sanctions inconsistent with the JCPOA, if Iran is willing to come back into compliance”.

He added the US was prepared to lift further sanctions if separate follow-on talks could reach agreement on Iranian regional behaviour and updated restrictions on Iran’s nuclear programme that went beyond the terms of the 2015 deal.

He said the two sides had made headway in the talks in Vienna but it was now an open question whether the Raisi administration had rejected the deal.

Mora will be demanding that the UN’s nuclear weapons watchdog the IAEA is invited within days to Iran for previously scheduled talks to discuss how it is to continue monitoring nuclear sites. The restrictions on the IAEA’s work is of unprecedented concern, Mora’s team said.