* Trump makes strongest comments yet on Khashoggi case

* Erdogan adviser - prince has blood on his hands

* Global outcry over death of veteran journalist

* Erdogan pledges guilty will face justice (Recasts with Crown Prince's remarks)

By Ali Kucukgocmen and Ezgi Erkoyun

ISTANBUL, Oct 24 (Reuters) - Saudi Arabia's crown prince said on Wednesday the case of Jamal Khashoggi was "painful" and that "justice will prevail" following the killing of the Saudi journalist at the Saudi consulate in Istanbul.

Appearing on a discussion panel at an international investment conference in Riyadh, Crown Prince Mohammed bin Salman said all culprits would be punished, and that Saudi Arabia and Turkey would work together "to reach results."

"The incident that happened is very painful, for all Saudis... The incident is not justifiable," he said.

"Justice in the end will appear."

Hours earlier U.S. President Donald Trump, in his toughest comments yet, told the Wall Street Journal that the crown prince bore ultimate responsibility for the operation that led to Khashoggi's killing.

Trump said he wanted to believe Prince Mohammed when he said that lower level officials were to blame for the killing at the Saudi mission.

But he suggested responsibility lay higher up: "Well, the prince is running things over there more so at this stage. He's running things and so if anybody were going to be, it would be him."

His comments heaped pressure on his close ally amid a global outcry over the journalist's death, and came hours before Prince Mohammed's appearance at a Saudi investment conference where he is due to make his most high profile comments since Khashoggi was killed on Oct. 2.

A number of high profile business and political figures have pulled out of the conference over the death of the journalist, a prominent critic of Saudi Arabia's de facto ruler.

Turkish President Tayyip Erdogan spoke to Prince Mohammed on Wednesday and the two discussed the steps needed to bring to light all aspects of the killing of Khashoggi, a presidential source said.

An adviser to Turkey's president said Prince Mohammed had "blood on his hands" over Khashoggi, the bluntest language yet from someone linked to Erdogan.

Saudi authorities did not immediately respond to a request for comment about the remarks by Trump and the Erdogan adviser.

Riyadh has blamed a "rogue operation" for the death of the prominent Saudi journalist and said the crown prince had no knowledge of the killing.

The death of Khashoggi, a U.S. resident and Washington Post columnist, has sparked global outrage and threatened relations between Riyadh and Washington as well as other Western nations.

For Saudi Arabia's allies, the burning question has been whether they believe that Prince Mohammed, who has painted himself as a reformer, has any culpability in the killing, a possibility raised by several U.S. lawmakers.

(Editing by William Maclean; Editing by Jon Boyle)

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