JERUSALEM - Stray mortar rounds and a tank shell fired from Syria landed in the Israeli-controlled Golan Heights on Thursday, causing alarm but no injuries or damage.

It was the third time in less than a week that spillover from the Syrian civil war had breached the demilitarized zone or crossed the decades-old armistice line between Israeli and Syrian forces. The United Nations has warned that the violence could jeopardize the cease-fire between the countries.

The tank shell, which did not explode, fell in Aloney Bashan, an Israeli village near the frontier, and two mortar shells exploded nearby, according to Israeli military officials.

The Israeli military said the fire had been errant and not directed at Israel. But touring the Golan Heights on Sunday, the military chief of staff, Lt. Gen. Benny Gantz, said of the fighting between the Syrian government and rebels, "This is a Syrian issue that could become our issue."

On Monday evening, an Israeli military vehicle traveling near the security fence along the frontier was hit and damaged by bullets that military officials said were most likely from the fighting inside Syria. There were no injuries.

Two days earlier, the U.N. observer force that monitors the cease-fire reported that Syrian armed forces were conducting operations against armed rebels with at least four battle tanks and mortar fire inside the demilitarized buffer zone. Israel lodged a complaint with the United Nations.

Martin Nesirky, spokesman for the U.N. secretary-general, Ban Ki-moon, told reporters in New York on Tuesday that the U.N. force in the area had not yet observed the battle tanks' leaving. The presence of military personnel and the military operations in the area of separation, he said, were "a grave violation of the 1974 Agreement on Disengagement between Israeli and Syrian forces."