The incident occurred at the Himonio site -- Orestiada district -- along the river, which separates the land borders of Greece and Turkey in the Thrace province.
Border guards came under fire as they detained 11 illegal migrants and a Turkish man identified as a migrant smuggler. Authorities believe an accomplice of the alleged smuggler fired with an assault rifle from the opposite river bank, taking advantage of the darkness and the thick riverside brush.
A boat used to ferry the illegal from the Turkish side onto Greek territory was also confiscated.
The incident marks the second time in roughly a week that migrant smugglers operating from Turkish territory have fired on patrols along the Greek side, with a Frontex unit comprised of German personnel fired on last time.