Iran and world powers are "likely" to agree Friday on the terms of extending a Sunday deadline to reach a nuclear deal, China's chief negotiator in talks in Vienna said.

"Yes, it is likely," Wang Qun told reporters, adding however it remained unclear how long the deadline would be extended by.

A German court ruled Wednesday that 4.5 million euros ($6.1 million) be paid from the estate of the late Princess Soraya of Iran to three French charities.

The French Red Cross, an animal protection group and an organisation for the rights of disabled people must equally share the money, which is part of the fortune of Soraya Esfandiary Bakhtiary, who died in Paris in 2001, the court in Cologne ruled.

U.S. Secretary of State John Kerry and his Iranian counterpart laid the groundwork Tuesday for the possible extension of a Sunday deadline to strike a historic nuclear deal after intense talks in Vienna.

Both Kerry and Mohammad Javad Zarif said however after two days of one-on-one discussions which failed to yield any major breakthrough that negotiators would still keep trying until the July 20 cut-off.

U.S. President Barack Obama told his Chinese counterpart Xi Jinping on Monday he was determined to constructively manage growing differences between their two nations, at a time of high tensions in the Pacific region.

In a telephone call, Obama and Xi also discussed the international effort to reach a deal on Iran's nuclear program in Vienna and the need to ensure North Korea complies with demands for it to dismantle its nuclear program, the White House said in a statement.

Iranian dissident Mehdi Khazali, who was serving a six-year prison sentence for acts against national security and spreading propaganda against the regime, has been freed on health grounds.

The official IRNA news agency quoted Khazali's lawyer as saying that the 48-year-old inmate was hospitalized after going on hunger strike, and that the authorities had decided he was too ill to return to jail.

U.S. Secretary of State John Kerry was to meet again Monday with his Iranian counterpart seeking to narrow serious gaps blocking a historic nuclear deal with a deadline just days away.

One of Kerry's goals in prolonging an overseas trip to visit Vienna was "to have in-depth discussions" with Iranian Foreign Minister Mohammad Javad Zarif and "to gauge Iran's willingness to make the critical choices it needs to make," a senior State Department official said.

Iran's chief negotiator in nuclear talks in Vienna warned Saturday that Tehran is ready to walk away if "excessive" Western demands cause a failure, eight days before a deadline for a deal.

Abbas Araqchi said however that he hoped that the attendance from Sunday of foreign ministers including U.S. Secretary of State John Kerry would help overcome "deep differences" that remain.

Several hundred people demonstrated in Iran's capital on Saturday to demand that state television boost "the culture of the veil and chastity" in its programming.

Protesters denounced the presence of "badly veiled" women in soap operas and said women wearing the traditional full-body chador were often depicted as poor and uncultivated.

Britain and Germany's foreign ministers will join U.S. Secretary of State John Kerry in Vienna this weekend to seek to bridge what Washington called "significant gaps" in ongoing nuclear talks with Iran, London and Berlin said Friday.

The negotiations between Iran and the five permanent members of the U.N. Security Council plus Germany, which last week entered the final straight, are aimed at forging a lasting deal with Iran meant to ease fears that the Islamic state might develop nuclear weapons.

Moscow said on Thursday there were signs of progress at talks between world powers and Tehran on Iran's nuclear program and that it expected to reach a compromise before a deadline later this month.

"The discussions are quite difficult, but there are clear signs of progress," foreign ministry spokesman Alexander Lukashevich said of the negotiations under way in Vienna.