Israeli ground forces advanced beyond the demilitarized zone on the Israel-Syria border over the weekend, marking their first open entry into Syrian territory since the October 1973 war, according to two Israeli officials who spoke anonymously to The New York Times.

The Israeli deployment came amid a successful effort by rebel groups in Syria to oust Bashar al-Assad from power, prompting neighboring states to prepare for more regional instability created by the sudden fall and flight of the Syrian president.

Israeli forces have taken control of the mountain peak of Mount Hermon on the Syrian side of the border, as well as several other locations deemed necessary to consolidate control of the region.

Lt. Gen. Hershey Halevi, the Israeli military chief of staff, appeared to confirm Saturday night that Israeli forces had moved beyond a demilitarized buffer zone in the Golan Heights, saying Israel had “deployed troops on Syrian territory,” though he did not elaborate further.

Israel has been operating covertly in Syria for several years amid its ongoing conflict with Hezbollah, the Iranian-backed Lebanese militant group that had fought in Syria in support of Assad’s now-toppled government.

Recently, the Israeli military had announced that it was targeting Hezbollah’s supply lines in the region. But the deployment of ground troops beyond the demilitarized zone in Syria marks a major policy shift, as it is the first open entry of Israeli military forces into Syrian territory since the 1974 ceasefire agreement that formally ended the last war between Israel and Syria.

The Israeli air force over the weekend also struck targets in Syria to destroy government military assets that could fall into the hands of rebel forces and are considered strategic threats by Israel, the two officials said.

The Syrian Observatory for Human Rights reported a series of Israeli airstrikes on Sunday in the eastern part of the country, specifying that the frequency of the strikes accelerated after the fall of President Bashar al-Assad.

According to the director of the Syrian Observatory, “Israel carried out air strikes against weapons depots and positions belonging to the ousted regime and Iranian-backed groups in Deir Ezzor province,” noting that strikes against these targets have increased since Assad left the country when jihadists seized the capital Damascus in a lightning offensive.