VIENNA: Diplomats paused international talks in Vienna on Friday aimed at the revival of the 2015 Iran nuclear deal, with European participants voicing "disappointment and concern" after five days of negotiation.

"Tehran is walking back almost all of the difficult compromises crafted after many months of hard work," said senior diplomats from the so-called E3 (Britain, France and Germany), referring to the previous rounds of talks between April and June.

Delegations from the talks will now return to their national capitals before talks restart in Vienna in the middle of next week "to see whether gaps can be closed or not", the diplomats said.

The E3 "remain fully committed to a diplomatic way forward," they added, but stressed that "time is running out".

The talks are aimed at reviving the 2015 nuclear deal, known as the JCPOA, which was initially agreed between Britain, China, France, Germany Iran, Russia and the United States.

The accord aimed at putting curbs on Iran's nuclear programme to ensure it couldn't develop an atomic weapon, in exchange for sanctions relief for Tehran.

Iran has always insisted that its nuclear programme is peaceful.

The deal began unravelling in 2018 when then US President Donald Trump pulled out of the deal and reimposed sanctions, prompting Iran to start exceeding limits on its nuclear programme the following year.

Trump's successor Joe Biden has said he wants to re-enter the deal and the US has been participating in this week's talks indirectly.

'Dragging their feet'

On Thursday the US had already issued a warning about the prospects for an agreement.

American Secretary of State Antony Blinken said that it was "not too late for Iran to reverse course" but insisted it could not "sustain the status quo of building their nuclear programme while dragging their feet on talks".

Israeli Prime Minister Naftali Bennett had used a call with Blinken to call for the "immediate cessation" of the nuclear talks, accusing Iran of "nuclear blackmail".

The talks had resumed in the Austrian capital on Monday after Iran paused them in June following the election of ultraconservative President Ebrahim Raisi.

During this week's talks Iran had submitted two draft proposals on sanctions lifting and nuclear-related measures.

The head of the Iranian delegation Ali Bagheri told the IRNA news agency Friday that the proposals were evidence "of our serious will to reach an agreement".

But acknowledging the frosty reception they had met with from the Europeans, he added: "I told them it's normal that we're not presenting documents and suggestions which correspond to your points of view".

European diplomats said there was "no path forward" based on the Iranian proposals.

The talks could resume in the middle of next week but speaking on a trip to the Gulf, French President Emmanuel Macron hinted that there could be a longer break before negotiators reconvene.

In a telephone call with EU top diplomat Josep Borrell, Foreign Minister Hossein Amir-Abdollahian said the talks were going well "but slowly on all tracks".

"We think that a good agreement is possible but that requires a change of approach by certain parties who must drop their threatening language and opt for texts focused on cooperation, mutual respect and results," the minister said.

Speaking after the end of Friday's talks, China's ambassador to the UN in Vienna Wang Qun struck a more positive note, saying that "all parties have reengaged themselves in very substantive terms".

He told reporters outside the Palais Coburg hotel where the talks have been taking place that he hoped the pause in talks "will help to provide further political impetus to the negotiations".