Amnesty International on Thursday called for an international investigation into the murder of Saudi journalist Jamal Khashoggi, in a ceremony marking the 100th day since his killing sparked global outrage.

“We once again call for an international investigation under the authority of the United Nations into the murder of Jamal Khashoggi,” Goksu Ozahishali, one of the rights group's Turkey representatives, said in a statement read out in front of the Saudi consulate in Istanbul, the scene of the murder.

In a case that shocked the world Khashoggi, a US resident and Riyadh critic who wrote for the Washington Post, was murdered and his corpse dismembered inside the kingdom's diplomatic compound on October 2.

“We demand justice for Jamal Khashoggi who fought for the freedom of expression in the Arab world,” Ozahishali said.

Amnesty activists later symbolically hung a street sign reading “Jamal Khashoggi Street” where the Saudi consulate is located.

Several questions remain unanswered including the whereabouts of Khashoggi's remains more than three months after the murder.

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“It's absolutely shocking that 100 days later there are no real concrete steps to bring this murder to justice,” Andrew Gardner, Amnesty's Turkey strategy and research manager, told AFP.

“Unfortunately the international community has been incredibly weak, and trade and diplomatic relations with Saudi Arabia have taken precedence over fundamental human values,” he said.

After evidence emerged that the killing was done by a team of Saudis sent from Riyadh and closely linked to Crown Prince Mohammed bin Salman, the international community demanded a transparent investigation.

Turkey and Saudi Arabia have opened separate investigations into the murder but Ankara has repeatedly accused Riyadh of failure to cooperate.

Turkish officials have blamed the crown prince for the killing, which the Saudi authorities categorically deny.

A trial opened last week in Saudi Arabia. The prosecutor has demanded the death penalty against five of the accused whose identities have not been revealed.