FOREIGN ATC CTLR DESCENDED MLG THROUGH ALT OF HVT WITH LESS THAN STANDARD SEPARATION CAUSING AN NMAC.

Narrative

ENRTE FROM CAIRO TO ATHENS; GREECE; S OF MILOS VOR I WAS GIVEN A DSCNT FROM FL350 TO FL280. THE CLRNC WAS TO FLY UA10 OVER MILOS; UA10 TO KEA VOR TO ATHENS. OVER MILOS VOR; WHILE DSNDING AT 1000 FPM TO FL280; ATHENS CTL ASKED ME TO INCREASE RATE OF DSCNT. ABOUT 5 SEC LATER; AN ACFT PASSED TO THE LEFT SIDE OF MY ACFT AT ABOUT THE SAME ALT. THE NMAC OCCURRED OVER THE MILOS VOR. THE CTLR CLRED MY ACFT THROUGH SOMEONE ELSE'S ALT. I FEEL THIS COULD HAVE BEEN AVOIDED IF THE CTLR HAD GIVEN ME A XING RESTRICTION 20 MI BEFORE (S) MILOS VOR. THE ACFT WERE NOT UNDER RADAR CTL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING. RPTR SAYS OTHER ACFT WAS HVT TYPE 4 ENG JET AND THINKS WAS ACR. ACFT WERE ON SAME FREQ AND OTHER ACFT ASKED ATC WHO WAS OFF HIS RIGHT AS ACFT PASSED. CTLR HAD JUST ASKED THE RPTR TO INCREASE HIS RATE OF DSCNT WHEN HE RPTED OVER MIL LEAVING FL290. NO RADAR ENVIRONMENT AND NO XING RESTRICTION WAS GIVEN NOR DID CTLR ASK FOR ANY ALT VACATING RPTS. RPTR GAVE FLT TIME OF 100 HRS LAST 90 DAYS AND 150 HRS IN TYPE. RPTR SAYS THIS IS BAD AREA TO FLY IN DUE TO LACK OF RADAR AND APPARENTLY LOOSE CTL.