SAUDI journalist Jamal Khashoggi’s “heinous murder” would have been unthinkable “without US backing,” Iranian President Hassan Rouhani said on Wednesday.

“I don’t think that any country would dare do such a thing without US backing,” Mr Rouhani said in remarks to cabinet broadcast on state television.

Mr Rouhani said that before Khashoggi’s murder “it would have been unthinkable that in this day and age we would witness such an organised felony.

“It is extremely significant that an institution planned such a heinous murder. The tribal group that is ruling that nation (Saudi Arabia) has a security margin. That security margin is that it relies on US backing. It is this superpower that is backing them.”

Khashoggi, a government critic who was living in self-imposed exile in the United States, was murdered inside the Saudi consulate in Istanbul on October 2 as he organised the paperwork for his marriage to his Turkish fiancee.

The case has triggered an international outcry against Saudi Arabia.

US President Donald Trump has ridiculed Riyadh’s response as “one of the worst cover-ups” in history.

Iran had been silent about the Khashoggi case until Monday when its judiciary chief slammed Saudi Arabia over his death.

“This heinous murder further revealed the nature of Saudis, their kingdom and that young man who is seeking fame and murdering innocent people,” Sadegh Amoli Larijani was quoted as saying by the judiciary’s news agency Mizan Online, apparently referring to Saudi Crown Prince Mohammad bin Salman.

Mr Trump has said Khashoggi’s death was a botched operation and a “bad original concept”.

His administration has taken its first steps in punishing the Saudis by deciding to revoke the visas of the suspects.

Mr Trump will get a briefing tomorrow from CIA Director Gina Haspel, who has been in Turkey.

“They had a very bad original concept,” Mr Trump said. “It was carried out poorly, and the cover-up was one of the worst cover-ups in the history of cover-ups. Somebody really messed up, and they had the worst cover-up ever.”

Mr Trump has resisted calls to cut off arms sales to the kingdom and has been reluctant to antagonise the Saudi rulers.

Mr Trump considers the Saudis vital allies in his Mideast agenda.

Members of Congress have demanded that sanctions be imposed on Saudi Arabia over the killing of Khashoggi.

Crown Prince Mohammed bin Salman has vowed to bring the killers of Khashoggi to justice, describing the case as “painful, horrible and unjustified” in his first public speech since the start of the crisis.

“Saudi Arabia is taking all legal measures ... and working with the Turkish government to reach results and bring all the criminals to justice,” the 33-year-old Saudi heir apparent told a major investment conference in Riyadh.

“Justice will prevail.”

Prince Mohammed said some people were trying to make use of Khashoggi’s case to “drive a wedge between Saudi Arabia and Turkey.”

Turkish President Recep Tayyip Erdogan said earlier on Wednesday that his country would not allow those responsible for the killing of Khashoggi to evade justice, maintaining pressure on the Saudi elite amid rising global criticism of Riyadh.

The Saudi leadership remains under immense international pressure over the murder of Khashoggi, with strong reactions from the EU and Australia on Wednesday.

Also on Wednesday, Erdogan and the Saudi crown prince had a telephone conversation about “joint efforts” to shed light on the killing of Khashoggi, according to Turkish state news agency Anadolu, marking the first contact between the Turkish and Saudi leaders since the start of the case.

Australia could follow Germany’s lead and suspend new arms sales to Saudi Arabia in response to the crime, Defence Minister Christopher Pyne said in Canberra.

France said it would apply sanctions against Saudi Arabia if the kingdom was clearly found responsible for the killing.

Iranian President Hassan Rowhani called on the United States and the European Union not to back down from putting pressure on Saudi Arabia - an arch-enemy of Iran.

Saudi authorities on Wednesday gave Turkish investigators the green light to search a well on the grounds of the Saudi consulate in Istanbul, Turkish state media reported.

Police had previously been denied access to the well on two separate occasions, Turkish state news agency Anadolu said, but various pro-government media outlets reported that the authorisation to search it was given on Wednesday.