Israel complained to U.N. peacekeepers over the incursion.
Lt. Gen. Benny Gantz told Israeli soldiers there Sunday to be on high alert, warning that violence from Syria's civil war might reach Israel.
Several Syrian shells, apparently misfired, have exploded inside Israel.
Israel captured the Golan Heights from Syria in the 1967 Mideast war. Before that, Syria used the highlands to shell Israeli villages below.
Israel annexed the strategic territory in 1981 in a move that is not recognized internationally.
The demilitarized zone was created after the 1973 Mideast war, when Syria tried to retake the plateau.