ANKARA- Turkey's foreign ministry has summoned Saudi Arabia's ambassador for consultations over the disappearance of journalist Jamal Khashoggi after he entered the Saudi consulate in Istanbul, Turkish sources said on Thursday.

They said the Saudi envoy was called in on Wednesday to clarify the whereabouts of Khashoggi, a critic of Riyadh's foreign policy and its crackdown on dissent who left Saudi Arabia last year saying he feared retribution for his views.

"Yesterday the Saudi ambassador was summoned to the foreign ministry and the issue of Khashoggi was discussed," one of the sources said. "Efforts are being made to clarify allegations about Khashoggi. We believe a positive outcome will emerge".

"Since yesterday, contacts have been continuing between Turkey and Saudi Arabia to overcome the problem related to Khashoggi," the source said.

Khashoggi's fiancée and a close friend said he vanished after entering the Saudi mission in Istanbul on Tuesday.

Saudi Arabia's Consulate General in Istanbul said in a statement on Wednesday that Khashoggi had left the consulate building shortly after his appointment on Tuesday.

It said the consulate was working with Turkish authorities "to uncover the circumstances" of his disappearance. No one at the Saudi embassy in Ankara was available to comment on Thursday and an official at the consulate, asked about the envoy's summons, referred back to the statement.

Khashoggi's disappearance could complicate already fraught ties between Ankara and Riyadh. Turkey has supported the Gulf state of Qatar in its prolonged stand-off with Saudi Arabia and its allies, sending troops to Qatar last year.

President Tayyip Erdogan's spokesman said on Wednesday Turkey believed Khashoggi was still inside the Saudi consulate in Istanbul, challenging the Saudi account.

Turkey has avoided public criticism of Saudi Arabia, a regional economic power due to its oil wealth and home of Islam's two holiest shrines.

(Reporting by Tulay Karadeniz and Orhan Coskun Writing by Tuvan Gumrukcu and Dominic Evans Editing by David Dolan and Jon Boyle) ((tuvan.gumrukcu@tr.com; +903122927021; Reuters Messaging: tuvan.gumrukcu.thomsonreuters.com@reuters.net))