Foreign Minister Mevlüt Çavuşoğlu said Saturday that Saudi authorities should cooperate to provide access for Turkish prosecutors and experts into the consulate premises for a sound investigation into the disappearance of journalist Jamal Khashoggi.

"Saudi Arabia needs to cooperate for the [Turkish] prosecution personnel and experts to enter the consulate premises for the soundness of this investigation and everything to come into light. We still have not seen cooperation in order to ensure a smooth investigation and bring everything to light. We want to see this," Çavuşoğlu told reporters in London.

According to the minister, there is a consensus on forming a joint working group with Saudi officials over the case of Khashoggi, who has not been seen since entering the Saudi Consulate in Istanbul on Oct. 2.

Turkey's top diplomat is in London to meet with his British counterpart Jeremy Hunt and to attend a roundtable meeting organized by the U.K.-based think-tank Chatham House.

'Consequences will certainly be serious'

On the probe of the Oct. 2 disappearance of journalist Jamal Khashoggi after entering the Saudi Consulate in Istanbul, spokesman for Justice and Development Party (AK Party) Ömer Çelik said: "There are very speculative claims on the murder of a respected journalist."

"There is a focus on some names, all of them are claims, all of them will be thoroughly investigated," he added.

Saying that murdering a journalist is an unforgivable act that cannot be covered up, he warned that if this happened, "the consequences will certainly be serious."

On the same day that the Saudi journalist arrived at the consulate, 15 other Saudis, including several officials, arrived in Istanbul on two planes and visited the building while Khashoggi was also inside, police sources said. All of the identified individuals have since left Turkey.

Saudi authorities have yet to give a clear explanation of Khashoggi's fate, while several countries — particularly Turkey, the U.S., and the U.K — are pressing the case to be cleared up as soon as possible.

On Thursday, Turkey said it and Saudi Arabia had agreed to form a joint working group — at Riyadh's initiative — to investigate the case. A Saudi source said a senior royal, Prince Khaled al-Faisal, had visited Turkey that day.

Khashoggi entered the Saudi consulate to get documents for his forthcoming marriage. Saudi officials say he left shortly afterwards but Turkish officials and his fiancee, who was waiting outside, said he never came out.

Turkish sources have told Reuters the initial assessment of the police was that Khashoggi, an outspoken critic of the Saudi government, had been deliberately killed inside the consulate. Riyadh has dismissed the claims.

The Saudi delegation, which arrived in Turkey on Thursday, is meeting a Turkish prosecutor investigating the case as well as representatives from the Justice Ministry, Interior Ministry, police and the national intelligence agency, one source said.

On Tuesday, the Turkish foreign ministry said the Saudi consulate in Istanbul would be searched as part of the investigation.