Israel’s ambassador to the UN sent a strongly worded letter to the secretary general of the UN and the UN Security Council president on Monday protesting a “grave violation” of the treaty between Israel and Syria.

Three Syrian tanks entered the demilitarized zone separating Israel and Syria on Saturday and on Monday an IDF jeep patrolling the Golan Heights was struck by gunfire from Syria.

Citing the 1974 Separation of Forces agreement, Ambassador Ron Prosor emphasized in his letters to UN Secretary-General Ban Ki-moon and to Security Council President Hardeep Singh Puri that Israel has so far shown great restraint. Nevertheless, he wrote that Syrian forces so close to the Israeli border “represents a dangerous escalation that could have far-reaching implications for the security and stability of our region.”

Prosor called on the UN to “address this alarming development without delay to prevent further escalation.”

The Israeli envoy claimed that this is not first time that Syria has recently violated the Separation of Forces agreement. In July, Israel lodged a complaint with the UN after Syrian troops entered the buffer zone between the two countries, and in September, mortars from Syria fell in the northern Golan Heights.

Both of those incidents, like the one on Monday, have been regarded by Israeli officials as spillover from the violence between the Syrian army and rebel forces attempting to topple the regime of President Bashar Assad. While officials do not believe the violence has been intentionally directed at Israel, IDF forces are currently in a state of heightened alert along the northern border.

“It is a Syrian issue,” Chief of General Staff Lt. Gen. Benny Gantz told a group of officers on Sunday. “But it can become ours.”