Hope among Iranians for a lasting deal over their country's nuclear programme gave way to frustration Wednesday as negotiations with world powers overran yet another deadline to seal a final accord.

The deal, which has been under negotiation for over 20 months, was originally meant to be struck by July 1. But the deadline has been extended twice, and marathon discussions in Vienna are expected to drag on until at least the weekend.

The streets of Tehran were largely empty Wednesday, with most of the country commemorating the death of Imam Ali, the key figure of Iran's Shiite Muslim faith.

But many Iranians were still anxiously awaiting news from Austria.

The agreement is "important for me because I want to make investments but I'm left confused and frustrated as to what the outcome of the negotiations will be," said 24-year-old architecture graduate Parnian.

She said she was "optimistic" about a deal but added that "things will not change for better" for ordinary Iranians.

"The status quo will be preserved after a deal and the best thing that can happen is that things won't get worse," she said.

Iran and world powers -- Britain, China, France, Germany, Russia, and the United States -- have been locked in negotiations for months seeking a lasting deal on Iran's nuclear programme.

The deal would curb Tehran's atomic capability, making it virtually impossible to build a nuclear bomb, in exchange for a lifting of punishing economic sanctions imposed on the Islamic republic since 2006.

Iran denies seeking a bomb and has called for sanctions to be dropped as soon as a deal is in place.

"I remain very positive and I believe that an agreement will be reached because the government of President Hassan Rouhani resumed negotiations believing a deal was possible, and they worked really hard for it," said Mohammad, a 31-year-old computer engineer from the northeastern city of Shahrud.

- Inflation, oil price plunge -

He said he had spent the last 12 days closely monitoring progress out of Vienna on television and social media.

"It's important to get it done as soon as possible, because the longer it takes, the more money and opportunities we lose" to boost the economy, Mohammad said.

If a deal is signed and sanctions are lifted, "the situation will improve, wages will increase and there will be more jobs," he predicted.

Middle class and poor Iranians have seen their purchasing power plummet since 2012, with inflation above 40 percent and a currency that had already lost two-thirds of its value before Rouhani took office.

The moderate leader managed to curb inflation to around 15 percent while under sanctions, but another challenge emerged last year as oil prices almost halved, as did state oil revenue.

The government has also reduced direct subsidies introduced by former President Mahmoud Ahmadinejad originally meant to mitigate price increases.

"In 2005, I earned two million rials a month and I could spend and save," recalls Mohammad. "Today, I earn between 15 to 20 million but my cheque barely gets me to the end of the month."

- 'There is hope' -

Since 2013, an interim accord that froze parts of Iran's nuclear programme in return for minor sanctions respite has been renewed twice already, and a "framework agreement" for a final text was reached in Lausanne in April.

The Vienna talks are supposed to be the last, but the going has been "very tough" as both sides edge closer to a lasting pact, according to one Western diplomat.

For Iranian journalist Emad Abshenass, "it is frustrating because the talks are taking so long. But as long as the talks are going on there is hope that they finally reach a deal, or even an agreement.

"Both sides are trying not to leave anything behind," he said.

Given the statements made by both sides ahead of the Vienna talks, Abshenass said "everyone" thought negotiations would go past the initial June 30 deadline.

"And even if the talks were to extend beyond July 10, they will find a way to solve the differences," he added.