While flying over serbia at fl 400, position 4352.2n/02237.8e, heading 290, some satellite like lights were observed traveling from west to east. on closer inspection, several of these lights were observed to be traveling in a straight line, one after the other, at constant distance, at a constant speed from west to east. two other crew members in cockpit observed the same. a broadcast was made on 121.5 for others in the area to observe. several pilots then responded seeing the same phenomenon. as many as 25 such lights were counted. they started to disappear as they went further into the earths shadow. the witnesses do not like to be named for obvious reasons. as it can be detrimental for aircrew from licensing point of view.