ISTANBUL (Reuters) - Turkey’s president insisted on Wednesday his country would not allow those responsible for Jamal Khashoggi’s killing to avoid justice, keeping up pressure on Riyadh amid global scepticism over varying Saudi accounts of the prominent journalist’s death.

FILE PHOTO: Saudi dissident Jamal Khashoggi speaks at an event hosted by Middle East Monitor in London Britain, September 29, 2018. Middle East Monitor/Handout via REUTERS/File Photo

President Donald Trump said on Tuesday Saudi authorities staged the “worst cover-up ever” in the killing of Khashoggi in Turkey this month, as the United States vowed to revoke the visas of some of those believed to be responsible.

“We are determined not to allow a cover-up of this murder and to make sure all those responsible - from those who ordered it to those who carried it out - will not be allowed to avoid justice,” Turkey’s President Tayyip Erdogan said in a speech in Ankara.

He said some people were uncomfortable with him sharing evidence in a speech on Tuesday about a killing stirring global outrage and straining ties between Riyadh and the West.

But he added: “We will continue to share new evidence transparently with our counterparts to enlighten the dark sides of this murder.”

On Tuesday Erdogan urged Riyadh to search “from top to bottom” to uncover those behind the death of the veteran Saudi journalist in the Saudi consulate in Istanbul on Oct. 2.

CIA Director Gina Haspel, in Turkey to investigate the death of Khashoggi, has sought to hear the purported audio recording of his torture and murder, four sources familiar with her mission told Reuters.

For Saudi Arabia’s allies, the question will be whether they believe that Crown Prince Mohammed bin Salman, who has painted himself as a reformer, has any culpability in the killing, a possibility raised by several U.S. lawmakers.

CONFLICTING ACCOUNTS

Saudi Arabia has given conflicting accounts about Khashoggi’s killing, first denying his death and later saying that Khashoggi - a U.S. resident and columnist for the Washington Post - died inside the consulate after a fight.

On Sunday Riyadh called the killing a “huge and grave mistake,” but sought to shield the crown prince from the widening crisis, saying Mohammed bin Salman had not been aware.

Saudi Arabia has detained 18 people and dismissed five senior government officials as part of the investigation. One of those fired includes Saud al-Qahtani, a top aide to Prince Mohammed. According to two intelligence sources, Qahtani ran Khashoggi’s killing by giving orders over Skype.

Turkish security sources say that when Khashoggi entered the consulate, he was seized by 15 Saudi intelligence operatives who had flown in on two jets just hours before.

The weeks of denial and lack of credible evidence in the face of allegations from Turkish officials that Khashoggi had been killed have shaken global confidence in ties with the world’s top oil exporter.

In the latest sign of unease, Swiss Foreign Minister Ignazio Cassis said the killing pointed clearly to a violation of human rights that required a review of Switzerland’s ties to Riyadh.

“On Monday, we demanded for a third time via a Saudi embassy employee that the affair be quickly explained,” Cassis told Swiss tabloid Blick. “Every day, we get another smidgen of new information. That’s regrettable.”

“The clues that are emerging centimeter by centimeter speak a clear language: A violation of human rights and the rule of law,” he added. “We have to ask ourselves the question of what that means for our bilateral relations. And we will definitely do that.”

Separately, President Hassan Rouhani of Iran, a regional rival of Saudi Arabia, said Riyadh would not have murdered Khashoggi without American protection, according to the Islamic Republic News Agency (IRNA).