Amnesty Internationalinfo-icon said on Sunday that reports of the murder of Saudi journalist Jamal Khashoggi in Turkeyinfo-icon would set an "abysmal new low" for Saudi Authorities.

Khashoggi, a contributor to the Washington Post, disappeared after going to the Saudi consulate in Istanbulinfo-icon on Tuesday to receive an official document for his marriage, and has not appeared since. 

Turkish police believe he was murdered inside Saudi Arabiainfo-icon's consulate by a team sent to Istanbul who left on the same day, a Turkish government source told AFP on Saturday.

"If true, this would be an abysmal new low," Amnesty International said in a statement.

"Such an assassination within the grounds of the Consulate, which is territory under Saudi Arabian jurisdiction, would amount to an extrajudicial execution."

The journalist went to the building to obtain official documents but "did not come back out", police were quoted as saying by Turkey's state-run Anadolu news agency.

I'm still at a loss to describe or find words for the Khashoggi alleged assassination. It's so brazen as to deserve words like stunning, shocking, unbelievable.

Ankara announced on Saturday it had opened an official probe into his disappearance.

Saudi Arabia "routinely uses draconian laws to crack down on peaceful dissent at home, and has even arrested dissidents abroad in the past," Amnesty said.  "But the enforced disappearance - and now reported assassination - of one of its citizens who had sought asylum abroad should set alarm bells ringing."

The alleged murder suggests that Saudi Arabia is "willing to dispense even with their own deeply flawed judicial proceedings in order to punish those who peacefully criticize them", the group added.

"The international community's deafening silence on Saudi Arabia's crackdown on freedom of expression must end and it must demand an immediate explanation from Saudi Arabia's authorities about Jamal Khashoggi's fate or whereabouts," Amnesty said.