Prominent journalist and Washington Post contributor Jamal Khashoggi was reportedly killed at the Saudi consulate in Istanbul in what the paper's sources are calling “a preplanned murder.”

The Washington Post reported Saturday, citing two sources familiar with the investigation, that the Kingdom allegedly sent a 15-member team to carry out the “preplanned murder.”

The Post said that neither source provided evidence to support this claim.

Khashoggi, 59, was reported missing on Tuesday while visiting the consulate for paperwork needed to marry his Turkish fiancée. He was living in the U.S. for the past year in self-imposed exile following the ascension of Prince Mohammed, now next in line to succeed his father, the 82-year-old King Salman.

The consulate insists that Khashoggi left the premises.

The longtime Saudi journalist and columnist has often been at odds with the ultraconservative Sunni Kingdom.

Khashoggi was known for his interviews and travels with Usama bin Laden between 1987 and 1995, including in Afghanistan, where he wrote about the battle against the Soviet occupation. In the early 1990s, he tried to persuade bin Laden to reconcile with the Saudi royal family and return home from his base in Sudan, but the al-Qaeda leader refused.

Khashoggi maintained ties with Saudi elites, including those in its intelligence apparatus, and launched a satellite news channel, Al-Arab, from Bahrain in 2015 with the backing of Saudi billionaire Prince Alwaleed bin Talal. The channel was on air for less than 11 hours before it was shut down. Its billionaire backer was detained in a Ritz Carlton roundup overseen by Prince Mohammed in 2017.

The Turkish official news agency reported Saturday that the public prosecutor’s office has started an investigation into his disappearance and the rumors that Khashoggi was detained had “deepened.”

The Associated Press also reported, citing a Turkish official, that detectives' "initial assessment" was that Khashoggi was killed at the consulate. That source did not provide further information on the matter.

“If the reports of Jamal’s murder are true, it is a monstrous and unfathomable act,” Fred Hiatt, the director of The Post’s editorial page, said in a statement. “Jamal was — or, as we hope, is — a committed, courageous journalist.”

The disappearance of Khashoggi could threaten the already fragile relationship between Saudi Arabia and Turkey.

The Associated Press contributed to this report.