TEHRAN - Iran has quit nuclear talks with world powers, accusing Washington on Friday of going against the spirit of a landmark agreement reached last month by expanding its sanctions blacklist.

A spokesman for EU foreign policy chief Catherine Ashton, who represents the major powers in the talks, said both sides had headed home for consultations and that she expected the talks to resume soon.

But Iran’s chief nuclear negotiator Abbas Araqchi said the US move went against the spirit of the deal struck in Geneva under which the powers undertook to impose no further sanctions for six months.

Tehran was now weighing the “appropriate response”, he said. “America’s move is against the spirit of the Geneva deal,” Araqchi told the Fars news agency as his team headed back to Tehran from Vienna. “We are evaluating the situation and will make the appropriate response. “Such a measure is by no means constructive and we are seriously critical of it,” Araqchi later said on state television.

Under the deal, Iran agreed to freeze parts of its suspect nuclear programme for six months in return for some $7b in relief from Western sanctions as it negotiates a final, comprehensive accord to allay suspicions it seeks a weapons capability. Iranian negotiators quit the implementation talks late on their fourth day Thursday after Washington blacklisted a dozen companies and individuals for evading US sanctions.

Foreign ministry spokeswoman Marzieh Afkham, quoted by state news IRNA, said: “The consequences of this unstudied move is completely on the American government.”

The Mehr news agency quoted informed sources as saying that the “new American sanctions” were the reason for the interruption. “The negotiations were halted by Iranian delegation because of new American sanctions. The Iranian negotiating team has halted the talks at this stage and are headed back to the capital due to America’s lack of commitment to the agreement,” Mehr reported.

But a spokesman for the EU foreign policy chief said both sides needed to return home for consultations and that Iran’s move was not unilateral. “After four days of lengthy and detailed talks, reflecting the complexity of the technical issues discussed, it became clear that further work is needed,” Ashton’s spokesman Michael Mann said. “There will now be consultations in capitals, in the expectation that technical talks will continue soon,” he added. Under Iran’s deal struck with the P5+1 of Britain, China, France, Russia and the United States plus Germany, Washington agreed to refrain from imposing new sanctions on Iran.

Meanwhile, US Secretary of State John Kerry said Friday nuclear talks between world powers and Iran were expected to resume soon, after Tehran said it was quitting the negotiations. "We're making progress, but I think we're at a point in those talks where folks feel a need to consult, take a moment," Kerry told reporters in Tel Aviv.

"There is every expectation that talks are going to continue in the next few days," he said of the talks.

Iran on Friday accused Washington of going against the spirit of a landmark interim agreement reached last month by expanding its sanctions blacklist and quit implementation talks.

EU foreign policy chief Catherine Ashton said both sides had headed home for consultations.

Under the interim deal, Iran agreed to freeze parts of its suspect nuclear programme for six months in return for some $7 billion in relief from Western sanctions as it negotiates a final, comprehensive accord to allay suspicions it seeks a weapons capability.

Kerry said he had spoken with Ashton and said he expected "we will proceed to the full implementation of that plan."

"This is sort of the normal part of the process in developing the implementation plan," he said of the breach in talks.

Kerry remarks were delivered as he was leaving for Asia, after a series of meetings with Israeli and Palestinian leaders on their troubled peace process.