Turkish President Recep Tayyip Erdogan accused Saudi Arabian officials of attempting to cover up the murder of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul last month, saying that the “puppetmasters” behind his killing must be revealed.

A failure to punish the perpetrators could set a dangerous precedent, Erdogan warned in an op-ed published Friday in The Washington Post. He also offered a stark warning that “no one should dare commit” such an act on a NATO ally’s soil again or else face “severe consequences,” the nature of which he did not specify.

“Had this atrocity taken place in the United States or elsewhere, authorities in those countries would have gotten to the bottom of what happened,” Erdogan wrote. “It would be out of the question for us to act any other way.”

Erdogan has been publicly vocal in the weeks since Khashoggi’s killing, demanding answers from the Saudis as to who ordered the killing and the whereabouts of Khashoggi’s remains. He renewed those calls in his op-ed, and vowed that his country would continue to search for answers in the murder of Khashoggi, who Istanbul’s chief prosecutor said was strangled and dismembered soon after entering the Saudi consulate in Istanbul on Oct. 2.

Khashoggi, who wrote for the Post and lived in self-imposed exile in the United States, entered the diplomatic compound to handle routine paperwork needed to marry his Turkish fiancée, Hatice Cengiz.

Cengiz, a Turkish national, waited for her fiancé outside the compound. He never returned.

Erdogan’s column comes exactly a month after Khashoggi’s death and on the same day as Cengiz slammed President Donald Trump’s administration in the Post for its response to Khashoggi’s killing.

“Of all nations, the United States should be leading the way. …But the Trump administration has taken a position that is devoid of moral foundation,” wrote Cengiz, who last week declined Trump’s invitation to the White House..

On Friday, Cengiz spoke via video from London at a memorial service held for Khashoggi in Washington. Through a translator, she called on Trump to support Turkey’s legal efforts and to help discover the whereabouts of her fiance’s body.

“Nothing has relieved me of the pain from the atrocity that I experienced,” Cengiz said via video. “The most important reason for this is because his corpse has still not been found.”

At a memorial service for Khashoggi in London earlier in the week, Cengiz directed remarks at some of Trump’s statements following the disappearance and murder of Khashoggi that appeared to downplay what happened to the Post columnist and Saudi regime critic.

“He should not pave the way for a cover-up of my fiancé’s murder,” Cengiz said of Trump. “Let’s not let money taint our conscience and compromise our values.”

Soon after Khashoggi went missing, Trump initially accepted the denials from the Saudi royal family of any involvement in Khashoggi’s death and said the U.S. would be punishing itself if it canceled a $110 billion arms deal with Saudi Arabia. More recently, Trump described Saudi Arabia’s handling of the Khashoggi case as the “worst cover-up in the history of cover-ups.”

Khashoggi’s death has been met with worldwide condemnation, the latest of which includes a letter from PEN America urging United Nations Secretary-General Antonio-Guterres to launch an independent investigation into Khashoggi’s case, which it called a “grave violation of human rights.”

The letter was signed by a number of novelists, journalists, and actors including Meryl Streep, Bob Woodward, J.K. Rowling, and Nobel laureates, Mario Vargas Llosa and Orhan Pamuk.