Khashoggi, who wrote opinion columns for The Washington Post criticising Saudi policies, was killed and dismembered in the Saudi consulate in Istanbul.
On Friday, a US intelligence report found the crown prince had approved the killing and Washington imposed sanctions on some of those involved – but not the Saudi leader himself.
The Saudi government, which has denied any involvement by the crown prince, rejected the report’s findings.
“It is essential that the crown prince ... should be punished without delay,” Hatice Cengiz said on Twitter. “If the crown prince is not punished, it will forever signal that the main culprit can get away with murder which will endanger us all and be a stain on our humanity.”
Ms Cengiz added: “Starting with the Biden administration, it is vital for all world leaders to ask themselves if they are prepared to shake hands with a person whose culpability as a murderer has been proven.”
On Friday, US president Joe Biden’s administration imposed a visa ban on some Saudis believed to be involved in the Khashoggi killing and placed sanctions on others that would freeze their US assets and generally bar Americans from dealing with them.
Asked about criticism of Washington for not sanctioning the Saudi leader directly, Mr Biden said an announcement would be made, but did not provide details.
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