Chinese Foreign Minister Wang Yi speaks to journalists in front of the Palais Coburg hotel, the venue for nuclear talks in Vienna, Austria, July 13, 2015. [Photo/Xinhua]

OIL PRICES FALL

Oil markets appeared to be expecting a deal soon as benchmark Brent crude futures fell about 1.5 percent on the prospect that sanctions would soon be lifted, allowing Iran to expand oil sales into an already oversupplied market.

Diplomats said there were contingency plans for an announcement ceremony in the event of a deal, which would open the door to ending sanctions that have crippled Iran's economy, in exchange for at least a decade of curbs on its nuclear programme.

The Western powers in particular suspect Iran may have sought to use its civil nuclear programme as a cover to develop a nuclear weapons capability. Iran says the programme is solely for peaceful purposes.

If no agreement is clinched by midnight, the powers will need to extend the terms of an interim nuclear deal that has already been extended three times in two weeks.

Both the Americans and Iranians have said they are willing to walk away and they could also suspend the talks for a few weeks or months, though Iran has said it opposes this and Earnest said he was not aware of any plans for a break.

Among the biggest sticking points in the past week has been Iran's insistence that a United Nations Security Council arms embargo and ban on its ballistic missile programme dating from 2006 be lifted immediately if an agreement is reached.

Russia, which sells weapons to Iran, has publicly supported Tehran on the issue.

"99 PERCENT FINISHED"

Other problematic issues include access for inspectors to military sites in Iran, explanations from Tehran of past activity that might have been aimed at developing a nuclear weapon and the overall speed of sanctions relief.

Iran's Fars news agency reported that Iran was pushing for the draft UN Security Council resolution under discussion as part of the deal to explicitly state that Tehran's nuclear programme is legal.

"The parts of the deal are there," said a senior official from one of the six countries. "We still need to put the finishing touches together. All sides have to decide now. It's time to say 'Yes'."

A senior Iranian official said 99 percent of the issues had been resolved, adding: "With political will, we can finish the work late tonight and announce it tomorrow."

Israeli Prime Minister Benjamin Netanyahu's point-man on the Iranian talks, Energy Minister Yuval Steinitz, told Israel's Army Radio he was expecting an agreement on Monday or Tuesday. He reiterated Israel's opposition to the deal.

"What is being drafted, even if we managed to slightly improve it over the past year, is a bad agreement, full of loopholes," he said. "If we call it by its true name, they are selling the world's future for a questionable diplomatic achievement in the present."

Comments from both Republican and Democratic senators on Sunday suggested that any final deal would also face tough scrutiny in the US Congress.