U.S. Secretary of State John Kerry on Friday urged Iran to free Amir Hekmati, an American who served as a U.S. Marine, from four years of "unjust detention."

Saturday marks the fourth anniversary of Hekmati's imprisonment on what Kerry called "false espionage charges" while Hekmati was visiting relatives in the Islamic republic.

A billboard in central Tel Aviv announcing the opening of an Iranian embassy that met with disbelief and curiosity turned out to be a hoax, organizers of the eye-catching stunt have said.

"Opening here soon - Embassy of Iran in Israel," proclaimed the five-storey tall hoarding emblazoned with the Iranian and Israeli flags this week. 

Iran urged the United States Wednesday to release 19 Iranians detained on sanctions-related offenses, a day after ruling out a prisoner swap with a Washington Post reporter accused of espionage.

"We call on the American government and their judicial authorities to put an end to the detention of these individuals," foreign ministry spokeswoman Marzieh Afkham said.

Saudi King Salman will visit the United States next month for the first time since acceding the throne and following a rift over America's rapprochement with Iran, a diplomat said Wednesday.

The monarch, who pulled out of a Gulf leaders' summit with U.S. President Barack Obama in May at the last minute, would travel to Washington on September 4, the Saudi diplomat said.

Kuwait has summoned an Iranian envoy to protest Tehran's apparent offer of investment opportunities in the disputed Dorra gas field, state media reported Wednesday.

The move followed a report by the National Iranian Oil Company (NIOC) about investment possibilities in the Islamic republic, which "covered areas located near the Kuwaiti oilfield," the KUNA news agency said.

The eagerly awaited premiere of Iran's multimillion-dollar film "Muhammad" about the childhood of the prophet was postponed Wednesday for 24 hours due to technical problems, a spokesman said.

The huge production cost an estimated $40 million and took more than seven years to complete.

Syrian President Bashar Assad described on Tuesday as "legitimate" the presence of fighters from Hizbullah in Syria to back his forces against anti-regime gunmen.

"The difference (between Hizbullah and foreign anti-regime fighters) is legitimacy. Who invited Hizbullah to Syria?" Assad asked. 

Dozens of hardline Iranian students opposed to the nuclear agreement with world powers gathered in front of parliament Tuesday, urging lawmakers to decide quickly on the text, several local media reported.

The nuclear deal would see sanctions on Iran lifted in exchange for a new inspections regime and curbs on the country's atomic program.

The U.N. atomic watchdog chief sought Tuesday to ease concerns in the United States about its investigation into Iran's alleged past nuclear activities following July's landmark deal with major powers.

"The arrangements made with Iran are technically sound and consistent with IAEA safeguards practices. They do not compromise our standards in any way," International Atomic Energy Agency chief Yukiya Amano said at a meeting in Vienna.

Iran's President Hassan Rouhani said Monday that world powers will eventually look back at last month's nuclear deal as a wise precursor to better relations with the Islamic republic.

His remarks came in a meeting with Britain's Foreign Secretary Philip Hammond, who is on the second and final day of a trip to Tehran.