A mortar shell fired on Tuesday during fighting between Syrian forces and rebels landed in the Israeli-occupied Golan Heights, Israeli military sources said.
It was unclear if the shell, which landed near an Israeli settlement and caused no injuries, was fired deliberately at territory held by Israel or was a stray, the sources said.
The U.N. Security Council voiced concern last week about the increasing spillover into the Golan Heights of the Syrian civil war being fought between forces loyal to President Bashar al-Assad and rebels trying to topple him.
Shells have fallen several times inside Israeli-controlled territory. Some incidents have drawn Israeli return fire.
Israel captured the Golan Heights from Syria in the 1967 Middle East war and annexed the strategic plateau in 1981 in a move that has not won international recognition. U.N. peacekeepers monitor the ceasefire line.
Israeli Defence Minister Moshe Yaalon, touring the Golan Heights earlier on Tuesday, said Israel would not intervene in Syria fighting unless it compromised Israeli security.
Israel is concerned Lebanon's Hezbollah guerrillas and al Qaeda could gain possession of Syria's chemical weapons. "We have acted against this and we will act in the future in order to prevent such weapons falling into the hands of irresponsible elements," Yaalon said.