JERUSALEM — Israeli forces in the Golan Heights fired into Syria on Sunday after a stray mortar round from fighting between Syrian troops and rebels hit an army post, the Israeli military said, calling the response a ‘‘warning.’’

The incident was said to be the first time Israel had fired across the Golan frontier into Syria since the 1973 Middle East war, and it underlined concerns that Syria’s civil war could draw in neighboring countries and trigger wider conflict in the region.