Explainer-What is the significance of the Golan Heights?

Israel denied on Tuesday it had advanced into Syria beyond a buffer zone with the Israeli-occupied Golan Heights since the overthrow of Syrian President Bashar al-Assad by rebel forces.

After his flight on Sunday ended 54 years of Assad family rule, Israeli troops moved into a demilitarised zone inside Syria set up after the 1973 Middle East war. Israel calls the incursion a temporary measure to ensure border security.

Following is a quick guide to the hilly, 1,200-square-kilometre (460 square-mile) Golan Heights, a fertile and strategic plateau that overlooks Israel's Galilee region as well as Lebanon, and borders Jordan.

WHY IS THE AREA CONTENTIOUS?

The Golan Heights were part of Syria until 1967, when Israel captured most of the plateau in the Six-Day War, occupying it and annexing it unilaterally in 1981. That annexation was not recognised by most countries. Syria still holds part of the Golan and has demanded that Israel withdraw from the rest of it. Israel has refused, citing security concerns.

Syria tried to regain the Golan in the 1973 Arab-Israeli war, but was thwarted. Israel and Syria signed an armistice in 1974 and the Golan has been relatively quiet since.

In 2000 Israel and Syria held their highest-level talks over a possible return of the Golan and a peace agreement. But the negotiations collapsed and subsequent talks also failed.

During U.S. President-elect Donald Trump's first term in 2019, he declared U.S. support for Israeli sovereignty over the Golan. The dramatic shift reflected Trump's decision in 2017 to recognise Jerusalem as the capital of Israel and move the U.S. Embassy to the city, which delighted Israel but infuriated Palestinians and many Arab political and religious leaders.

WHY DOES ISRAEL WANT THE GOLAN?

Security. Israel said earlier in Syria's more than decade-long civil war that it demonstrated the need to keep the plateau as a buffer zone between Israeli towns and the instability of its neighbour.

Israel's government also voiced concern that Iran, a longtime ally of the Assad regime, was trying to cement its presence on Syria's side of the border in order to launch attacks on Israel. Israel frequently bombed suspected Iranian military assets in Syria in the years leading up to Assad's fall.

Israel and Syria have both coveted the Golan's water resources and naturally fertile soil.

WHO LIVES THERE?

Some 55,000 people live on the Israeli-occupied Golan, about 24,000 of them Druze, an Arab minority who practice an offshoot of Islam, according to analyst Avraham Levine of the Alma Research and Education Center specialising in Israel's security challenges on its northern border. Many of the Druze adherents in Syria were long loyal to the Assad regime. Many families have members on both sides of the demarcation line.

After annexing the Golan, Israel gave the Druze the option of citizenship, but most rejected it and still identify as Syrian. Another 31,000 Israelis have settled there, Levine said. Many of them work in farming, including vineyards, and tourism.

WHO CONTROLS THE SYRIAN SIDE OF THE GOLAN?

Before the outbreak of Syria's civil war in 2011, there was an uneasy stand-off between Israeli and Syrian forces.

But in 2014 anti-government Islamist rebels overran Quneitra province on the Syrian side. The rebels forced Assad's forces to withdraw and also turned on U.N. forces in the area, forcing them to pull back from some of their positions.

The area remained under rebel control until the summer of 2018, when Assad's forces returned to the largely ruined city of Quneitra and the surrounding area following a Russian-backed offensive and a deal that allowed rebels to withdraw.

WHAT SEPARATES THE TWO SIDES ON THE GOLAN?

A United Nations Disengagement Observer Force (UNDOF) is stationed in camps and observation posts along the Golan, supported by military observers of the United Nations Truce Supervision Organization (UNTSO).

Between the Israeli and Syrian armies is a 400-square-km (155-square-mile) "Area of Separation" - often called a demilitarised zone - in which the two countries' armed forces are not permitted under the ceasefire arrangement.

The Separation of Forces Agreement of May 31, 1974, created an Alpha Line to the west of the area of separation, behind which Israeli military forces must remain, and a Bravo Line to the east behind which Syrian military forces must remain.

Extending 25 km (15 miles) beyond the "Area of Separation" on both sides is an "Area of Limitation" in which there are restrictions on the number of troops and number and kinds of weapons that both sides can have there.

There is one crossing point between the Israeli and Syrian sides, which until the Syrian civil war began was used mainly by United Nations forces, a limited number of Druze civilians and for the transport of agricultural produce.

(Writing by Mark Heinrich; editing by Howard Goller)