The countdown to the end of the six-month-long talks in Vienna on the future of the Iran nuclear deal has begun. No deadline has been formally set, but if there is no progress in less than two weeks the process will come to an end leaving a dangerous vacuum.

The White House has already been rolling the pitch preparing its political lines for a breakdown by saying the US withdrawal from the agreement by Donald Trump in 2018 has proved to be a disaster. If there is no agreement, the Biden team intend Trump will take the blame.

Ned Price, the US state department spokesperson, warned: “The runway is very, very short – weeks not months.” Antony Blinken, the secretary of state, has given the same time frame but said such are the advances in Iran’s nuclear programme, including levels of uranium enrichment at 60%, faster progress is needed.

Those close to the talks say they think there can be an agreement, but that from a western perspective it will possibly be so limited in scope it is will be seen as temporary. If so, as Enrique Mora, the chief EU negotiator has said, it will not be for lack of trying.

Surrounded by the gilt of the Palais Coborg hotel in Vienna, the large and expert teams of negotiators meet daily in different permutations delivering non-papers to one another. The one thing that is constant is that Iran refuses to meet the US negotiators, so discussions are carried out indirectly via the European, Chinese and Russian delegations.

Full-scale talks will resume on Monday, with both the UK and Germany represented by new chief negotiators, Stephanie Al-Qaq and Tjorven Bellmann respectively. Detail on progress is being kept to a minimum. Mikhail Ulyanov, the Twitter-happy Russian ambassador to the talks and a key interlocutor, occasionally sends out cryptic tweets designed to give a sense of momentum.

There are occasional noises off, quite literally. Explosions across western Iran on Saturday night, the Iranian government assured a jumpy nation, were explained by lightning, not an Israeli attack. But the Israeli prime minister, Naftali Bennett, has warned his country will not be bound by any agreement.

Others are also seeking to influence the balance of forces in Vienna.

A cast list of sceptical Gulf ambassadors have shown up to be briefed by the US special envoy, Robert Malley.

The Iranian foreign minister, Hossein Amir-Abdollahian, travelled to China to secure a 25-year partnership agreement, a move designed to show the inflation-wracked Iranian economy can if necessary survive without the west. Ebrahim Raisi, the Iranian president, will travel to Moscow this week with the same purpose.

Meanwhile, Evin prison’s terrifying revolving door keeps turning, with Iranians linked to the west being either reprieved or punished. One morning last week, Aras Amiri, a British Council employee, was released to return to the UK – the final hiccup was a Home Office demand she pay £1,000 to renew her expired indefinite leave to remain visa. But later that afternoon it was announced the French-Iranian academic Fariba Adelkhah had her furlough withdrawn and was ordered to return to Evin, a possible punishment for the French being deemed by Iran to be the bad boys of the E3 talks in Vienna.

From interviews and briefings Iranian officials have given at home, the sticking points are clear.

On lifting sanctions differences remain on how to classify whether a sanction relates to the nuclear deal, and so now should be lifted, or is related to other issues, such as Iranian terrorism or human rights abuses that the US and others say must remain in place.

A second issue surrounds the guarantees Iran is seeking that the US will not repeat Trump’s withdrawal from the deal in May 2018. The US cannot offer a legally binding treaty since the Senate would never agree to one. Price said: “There is no such thing as a guarantee in diplomacy and international affairs. We can speak for this administration, but this administration has been very clear that we are prepared to return to full compliance with the JCPOA [Joint Comprehensive Plan of Action] and to stay in full compliance with the JCPOA as long as Iran does the same.”

A UN security council resolution might be a bare minimum of comfort for Iran, but is hardly binding on the parties. Tehran wants binding commitments that if the US quits the deal, the EU will do more to defy secondary US sanctions by injecting real cash into the abortive trading mechanism Instex set up by the EU to bypass US sanctions.

A third issue is verification. What are the metrics by which Iran can verify that sanctions have been lifted in reality and not just on paper, and consequently that it must stop enriching uranium at levels of purity not allowed under the agreement? There has been loose talk that the US believes the lifting of sanctions could be verified in 48 hours, but Iran wants a longer process with benchmarks.

The final issue is how to handle both the technical knowledge, including advanced centrifuges and large amounts of enriched uranium that Iran has acquired during the period it has ended its commitments to the JCPOA.