Syrian troops entered the demilitarized buffer zone with Israel last week, during fighting with rebel groups near the Golan Heights.

Following the incident, Israel issued a complaint to the UN, Haaretz reported Sunday.

The penetration occurred last Thursday. Syrian troops entered the demilitarized zone near the Druze village of Mas’ade in the northern Golan Heights, apparently during clashes with rebel forces.

Defense Minister Ehud Barak, visiting the area Thursday, said he heard battles between Syrian troops and opposition forces taking place across the border.

Barak noted that the clashes were taking place “200 meters away from the UN forces and 800 meters from the fence”, not realizing, at that moment, the Syrian troops had entered the demilitarized zone.

Over the weekend, rebel forces managed to take control of the village of Rawyahina near Quneitra, only a couple kilometers from the border with Israel.

The demilitarized zone is the result of a disengagement agreement between Israel and Syria from 1974. A buffer zone of 3-6 kilometers was set, free of Israeli and Syrian armed forces and subject to military supervision by UN forces and Syrian civilian administration.

A UN force of 8,000 soldiers from Canada, Poland, Finland and Austria monitors the buffer zone on both sides of the border.

A Foreign Ministry source said Israel viewed the incident as a serious violation of the agreement, especially given the current instability in Syria.

Israel issued a strongly worded letter of complaint to UN Secretary General Ban Ki-moon and Néstor Osorio Londoño, the rotating president of the UN Security Council, Haaretz reported.

An Israel Defense Forces spokesperson said the army is maintaining “regular monitoring” of fighting on the border and is “conscious of the complex situation.”

Mitch Ginsburg responded to this report.