U.S. Special Envoy for Iran Robert Malley said on Sunday he was not confident that a nuclear deal between world powers and Tehran was imminent, dampening expectations after 11 months of talks in Vienna that have stalled.

The failure of efforts to restore a 2015 accord, which would curb Tehran's nuclear programme in exchange for lifting sanctions that have hammered Iran's economy, risks spiking political tensions in the Middle East and further increasing world oil prices, analysts say.

"I can't be confident it is imminent... A few months ago we thought we were pretty close as well," Malley said at the Doha Forum international conference.

"In any negotiations, when there's issues that remain open for so long, it tells you something about how hard it is to bridge the gap."

His assessment of the negotiations in Vienna came after Kamal Kharrazi, a senior advisor to Iran's Supreme Leader Ayatollah Ali Khamenei, said a deal could come soon.

"Yes, it's imminent. It depends on the political will of the United States," Kharrazi told the conference.

LAST MINUTE DEMANDS

Then-U.S. President Donald Trump abandoned the nuclear pact in 2018, prompting Tehran to start breaking nuclear limits set under the deal. Months of on-and-off talks to revive the deal were delayed earlier this month as Russia wanted guarantees it would be able to carry out its work as a party to the deal.

But there are still outstanding issues. Kharrazi said in order for the deal to be revived Washington must remove the foreign terrorist organisation (FTO) designation against Iran's Islamic Revolutionary Guard Corps (IRGC).

The IRGC, created by the Islamic Republic's late founder Ayatollah Ruhollah Khomeini, is more than just a military force and has enormous political clout. It was placed under sanctions in 2017 and put on the FTO list in April of 2019.

"IRGC is a national army and a national army being listed as a terrorist group certainly is not acceptable," said Kharrazi.

Malley said regardless of what happens, many sanctions on the IRGC will remain.

IRAN SEEKING GUARANTEE

Tehran has also been pushing for guarantees that any future U.S. president would not withdraw from the deal and the extent to which sanctions would be rolled back is another unresolved issue.

The United States' allies in the Gulf and Israel remain of the view that Tehran is a security threat and have deep misgivings over the talks.

Israel and the United States will continue to cooperate in preventing a nuclear-armed Iran, Israel's foreign minister said on Sunday.

"We have disagreements about a nuclear agreement and its consequences, but open and honest dialogue is part of the strength of our friendship," Yair Lapid said in Jerusalem during a joint press conference with visiting U.S. Secretary of State Antony Blinken.

Blinken said a return to the 2015 deal is the best way to contain Iran's nuclear programme.

But whether or not that happens, "our commitment to the core principle of Iran never acquiring a nuclear weapon is unwavering," he said.

The issue is likely to dominate a two-day summit in Israel which will include foreign ministers from three Arab states.

In Tehran, EU envoy Enrique Mora, who is the coordinator of the talks, met with Iran's chief nuclear negotiator Ali Bagheri Kani on Sunday to discuss pending issues in the nuclear talks.