Antwerp World Diamond Centre (AWDC) Chief Executive Ari Epstein resigned unexpectedly on Thursday, the AWDC’s board of directors said in a statement.

A spokesperson for AWDC, Belgium’s main diamond industry group, said on Friday that Epstein, who had been CEO for 13 years, did not wish to communicate about the reason for his sudden departure, but Belgian financial newspaper De Tijd reported that Russian diamond sanctions had been the cause of conflict between the diamond sector and the Belgian government.

AWDC did not say who would replace Epstein as CEO. Epstein did not immediately respond to a request for comment sent via LinkedIn.

Following an EU ban on Russian-origin diamonds that took effect on March 1, rough and polished diamonds have to enter the EU and G7 countries with documentary proof and declarations that the stones are not of Russian origin.

Antwerp’s diamond dealers have said they are facing long and costly delays as a consequence.