The French Foreign Ministry announced on Thursday that it was imposing sanctions against 18 Saudi citizens over the brutal murder of Washington Post columnist Jamal Khashoggi in Istanbul last month.

“These measures … aim to prohibit these individuals from entering national territory and the entire Schengen area” of Europe, the ministry said in a statement.

“They are conservative measures, subject to review or extension based on the findings of the investigation under way.”

Saudi officials have said that 21 people are in custody, with death penalties being sought against five men.

There is growing international pressure on Riyadh to find those responsible for the grisly murder of Khashoggi, a US resident who had been critical of Saudi Crown Prince Mohammad bin Salman.

A recent CIA analysis implicates Prince Mohammad, but Saudi prosecutors insist he had no role in the crime.

The US Treasury has imposed sanctions on 17 people, including close aides of Prince Mohammad, and Germany imposed similar measures on Monday.

– With reporting from Agence France-Presse