DAMASCUS — The United Nations has accused Israel of “severe violations” of a 50-year-old agreement with Syria, saying it has engaged in “engineering groundwork activities” that encroach on a key buffer zone in the Golan Heights.

“Violations of the 1974 Disengagement Agreement have occurred where engineering works have encroached into the AoS (the area of separation),” the UN Disengagement Observer Force (UNDOF), which has maintained the ceasefire between Israel and Syria since 1974, said in a statement Tuesday.

Satellite imagery from Planet Labs and the European Space Agency shows that the Israel Defense Forces (IDF) has been conducting excavation activity near Jubata Al Khashab, Syria since mid-August. A large earthen berm, roughly 40 feet (12 meters) wide, is being dug.

The trench now stretches almost five miles (eight kilometers).

Work on extending the trench even further is continuing, according to recent satellite imagery. In a Planet Labs image taken on November 5, an excavator and other vehicles can be seen working.

The “extensive engineering groundwork activities” run along the so-called Alpha Line that separates Syria and the Israeli-occupied Golan Heights, UNDOF said, adding that the construction began in July and includes the use of “excavators and other earth-moving equipment with protection from armored vehicles and soldiers.” Main battle tanks of the IDF were also occasionally present in the demilitarized zone, violating the 1974 agreement.

The UN peacekeeping mission said it has “repeatedly engaged with the IDF to protest the construction” work, which has worried Syrian authorities, who have also “strongly protested.”

UNDOF warned on Tuesday that Israel’s “severe violations” at the buffer zone “have the potential to increase tensions in the area.”

The peacekeeping force and its mandate were born out of a US-brokered ceasefire between Israel and Syria in May 1974, following months of fighting in a war launched by Egyptian and Syrian forces against Israel in October 1973.

The agreement created a buffer zone, as well as two equal zones of limited forces and armaments on both sides of the area. While Israel and Syria remain formally at war, this agreement has largely maintained peace with the help of the UN peacekeeping mission in the Golan.

For Israel, the Golan Heights is a strategic plateau seized from Syria during the Six-Day War in 1967, and formally annexed in 1981. The hilly landscape, which spans some 500 square miles, is home to some 20,000 Arab Druze and about 25,000 Jewish Israelis spread across more than 30 settlements.

It also shares a border with Jordan and Lebanon, where Israel has been waging a war against the Iran-backed Hezbollah group.

Israel sees the Golan Heights as key to its national security interests and says it needs to control the region to fend off threats from Syria and Iranian proxy groups there.

On Tuesday, UNDOF said that upon engaging Israel about the violations, the Israeli side said the construction is “being carried out for defensive purpose to prevent unauthorized crossing and violations by civilians” along the Alpha Line on the Israeli side.

Navvar Saban, a researcher at the Harmoon Center for Contemporary Studies who specializes in Iranian influence in Syria and Iraq, said Israeli activities in the Golan are likely for defensive purposes, as the IDF seeks to enhance its existing structures.

Israeli security forces and local residents gather at a site where a reported strike from Lebanon fell in Majdal Shams village in the Israeli-annexed Golan area on Saturday.

“This can be considered a precautionary move from the Israeli side for any possible increased operations from Hezbollah militias in that area,” Saban told CNN.

Israel has for months been conducting strikes inside Syria, saying it is targeting Iranian or Hezbollah interests. In April, following an Israeli strike on what Tehran said was a diplomatic building in Damascus, Iran responded by launching a barrage of missiles and drones directly at Israel.

In July, tensions between Israel and Hezbollah spiked after a deadly rocket attack hit a soccer field in the Arab town of Majdal Shams in the Golan, killing at least 12 children. Israel blamed Hezbollah for the attack, which the Lebanese group denied.

The Israeli military on Wednesday said it had struck “smuggling routes” between Lebanon and Syria, that it alleges were used to transfer weapons to Hezbollah.

The Israeli military said the strikes were part of a larger effort to target the capabilities of a Hezbollah unit responsible for weapons smuggling. The IDF also accused the Syrian regime of abusing civilian infrastructure for its support to Hezbollah. CNN has reached out to the Syrian Foreign Ministry and the Defense Ministry for comment.

The Syrian defense ministry earlier on Wednesday said an Israeli strike targeted bridges over the Orontes River and roads on the Syria-Lebanon border in the Qusayr area of the Homs countryside in western Syria. The strike “caused significant damage to these bridges and roads, rendering them out of service,” the ministry said.

Saban said that Hezbollah is unlikely to try and trigger an Israeli military offensive from the Golan, however.

“Syria is the only remaining backdoor for Hezbollah,” he told CNN, adding that Hezbollah has not operated in the area against Israel the way it has from southern Lebanon. The group cannot handle the “shock” of another front from the Israelis, he said.

Israel has in recent months accused Syria of violating the 1974 agreement. In July, the IDF said it struck Syrian military infrastructure in retaliation for alleged breaches. “The IDF holds the Syrian military responsible for all activities occurring within its territory and will not allow any attempts to violate Israeli sovereignty,” the Israeli military said. — CNN