RNA - The UK-based rights body made the demand Thursday during a ceremony outside the Saudi consulate in Istanbul where the incident took place last October to mark 100 days since the murder.
"We once again call for an international investigation under the authority of the United Nations into the murder of Jamal Khashoggi," Amnesty's Turkey representative Goksu Ozahishali said.
"We demand justice for Jamal Khashoggi who fought for the freedom of expression in the Arab world," she added.
The Washington Post columnist, who would regularly bash Saudi Crown Prince Mohammed bin Salman in his articles, entered the diplomatic mission to secure documents for a pending marriage but never came out.
Murder site dubbed 'Khashoggi Street'
Amnesty activists on Thursday symbolically hung a street sign reading "Jamal Khashoggi Street" where the consulate is located.
"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.
Evidence has shown that the killing was carried out by a hit squad with close links to bin Salman, and Turkish officials have blamed the royal for the death.