Agonizing talks towards a grand bargain nuclear deal between Iran and major powers looked set Thursday to drag into the weekend and beyond, with stubborn differences still separating the two sides in Vienna.

There was little indication meanwhile whether the head of the U.N. atomic watchdog had made any progress in Tehran on one of the main sticking points: a probe into allegations of past nuclear westernization work.

China's foreign minister said Thursday that he sees a "high possibility" of Iran and major powers agreeing a nuclear deal, but said all sides need to make "positive efforts."

"Hopefully a consensus can be reached among the parties. All parties concerned need to work together to uphold the international non-proliferation regime and help deliver a solution to this long-standing nuclear issue," Wang Yi said.

World powers negotiating a deal with Iran to curb its nuclear ambitions were grappling for a breakthrough as last-ditch talks dragged into a sixth day Thursday.

With the diplomatic drive playing out both in Vienna and Tehran, ministers held a flurry of meetings as the clock ticked down to a new July 7 deadline.

Iran said Wednesday it has recovered part of its gold reserves frozen under international sanctions after an accord sealed on the sidelines of nuclear negotiations with world powers.

Central bank chief Valiollah Seif, quoted by state news agency IRNA, said the accord covers the repatriation of a total of 13 tons of gold blocked in South Africa for the past two years.

Talks between Iran and major powers towards a historic nuclear deal are facing tough issues but are making progress, U.S. Secretary of State John Kerry said Wednesday during a break from talks in Vienna.

"We are working very, very hard and we have some very difficult issues but we believe we're making progress and we're going to continue to work because of that," Kerry told reporters.

Intense negotiations between Iran and major world powers ramped up Wednesday with the chief of the U.N. atomic watchdog heading to Tehran for talks on a nuclear bomb probe vital for a deal.

U.S. Secretary of State John Kerry and his Iranian counterpart held fresh negotiations in Vienna seeking to narrow differences before the new deadline of July 7 announced on Tuesday.

Israel has fired the latest shot in its campaign against the impending deal on Iran's nuclear program, with an animated video comparing the Islamic republic to the Islamic State group.

"The Islamic state of Iran -- like ISIS. Just much bigger," is the title and punchline of the cartoon clip posted on Tuesday on Prime Minister Benjamin Netanyahu's official Twitter account.

Iran's supreme leader Ayatollah Ali Khamenei on Tuesday unveiled the main points of the Islamic republic's next five-year plan, with the focus on the military and economic growth.

According to extracts published by the official IRNA news agency, the 2016-2021 plan allocates at least five percent of the budget to defense "as part of the regional balance of power" and to protect national interests.

Drought-hit North Korea on Tuesday asked for humanitarian aid from its historic ally Iran, Iranian state media reported.

North Korean Ambassador Kang Sam-hyon delivered a request to the Iranian Red Crescent for urgent humanitarian aid to combat what Pyongyang has termed its worst drought in 100 years, aggravating dire food shortages, state news agency IRNA said.

Iran and six major powers on Tuesday gave themselves until July 7 to clinch a historic nuclear deal as a midnight deadline approached in marathon talks with no breakthrough in sight.

Russian Foreign Minister Sergei Lavrov, who joined the talks in Vienna earlier Tuesday, said however he believes that, after almost two years of trying, a deal ending the 13-year standoff is "within reach."