Shortly after Syrian president Bashar al-Assad's overthrow by rebel forces, Israel ordered its troops to enter a demilitarised buffer zone situated along the east of Syria's Golan Heights plateau it controls.
Israel's occupation of the Golan Heights is not recognised by any country other than the United States, and the IDF's deployment in the buffer zone outside of it effectively amounts to Israel driving deeper into Syrian territory.
The zone, known as the Area of Separation, was set up as an area of no military engagement after the 1973 Middle East war.
Israeli leaders denied the IDF had advanced into Syria beyond the established boundaries and called the incursion a temporary measure to ensure border security.
Here is a quick guide to the hilly, 1,200-square-kilometre Golan Heights, a fertile and strategic plateau that overlooks Israel's Galilee region as well as Lebanon, and borders Jordan.
Why the area is contentious
The Golan Heights was part of Syria until 1967, when Israel captured most of the plateau in the Six-Day War, also known as the 1967 Arab-Israeli War, occupying it and annexing it unilaterally in 1981.
That annexation was not internationally recognised, including by the US, until 2019 when then-US president Donald Trump declared American support for Israeli sovereignty over the Golan Heights.
The dramatic shift reflected Trump's decision in 2017 to recognise Jerusalem as the capital of Israel and move the US Embassy to the city, which delighted Israel but infuriated Palestinians and many Arab political and religious leaders.
Syria still holds part of the Golan Heights and has demanded that Israel withdraw from the rest of it. Israel has refused, citing security concerns.
[MAP]Syria tried to regain the Golan Heights in the 1973 Arab-Israeli War but was thwarted. Israel and Syria signed an armistice, or Disengagement Agreement, in May 1974, and the region has been relatively quiet since.
The deal mandated the two nations to "scrupulously" observe a ceasefire on land, sea and air and saw the creation of a buffer zone which neither Israeli nor Syrian military forces could enter.
A United Nations Disengagement Observer Force (UNDOF) was established for peacekeeping in the 400-square-kilometre area, which can only have UNDOF personnel stationed within it.
Its vicinity is considered Syrian territory and houses many Syrian villages within it.
In 2000, Israel and Syria held their highest-level talks over a possible return of the territory and a peace agreement. But the negotiations collapsed and subsequent talks also failed.
Why Israel wants the Golan Heights
Israel says its primary interest is its own security.
Prime Minister Benjamin Netanyahu's government had said earlier that Syria's civil war, lasting more than a decade, demonstrated the need to keep the plateau as a buffer zone between Israeli towns and the instability of its neighbour.
It 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.
But the Golan Heights is also a great strategic asset to Israel and Syria.
Both have coveted the territory's water resources and naturally fertile soil, and with its high elevation, it serves as a crucial vantage point over northern Israel to the west and the Syrian capital of Damascus to the north-east, aiding Israel's monitoring of enemy movements.
The territory is home to Mount Hermon, Syria's highest peak, and is also well within sight of Lebanese border regions, including the Hezbollah-held Beqaa Valley.
"Over the years, Israel has established a series of monitoring posts and electronic listening devices on Golan that are too vital to be compromised," Middle East analyst PR Kumaraswamy wrote in a peer-reviewed paper.
"From a purely military-strategic point of view, Israeli control and domination of high grounds on Golan are considered essential for the defence of Galilee Panhandle along the Israeli-Lebanese border and the Israeli shores of the Sea of Galilee."
Why Israel entered the buffer zone
In response to criticism of Israeli troops entering the buffer zone over the weekend, Mr Netanyahu insisted the move was "defensive" in the face of risks likely to arise from the Syrian rebel takeover.
"We have no intention of interfering in Syria's internal affairs, but we clearly intend to do what is necessary to ensure our security," the Israeli PM said.
Several Arab nations characterised the move as an opportunistic land grab. UN spokesman Stephane Dujarric and the UN's Special Envoy for Syria also said it violated terms of the 1974 ceasefire deal.
Danny Danon, the Israeli ambassador to the UN, wrote in a letter to the UNSC that armed groups had entered the Area of Separation on December 7, targeting UNDOF forces, temporarily taking control of UNDOF outposts, and looting their equipment.
"In response to this evolving security threat and the danger posed by it to Israel — particularly to the residents of the Golan Heights — Israel has taken limited and temporary measures to counter any further threat to its citizens," he said.
Mr Dujarric also acknowledged this incident.
"Armed individuals climbed the wall of a UN position near Hadar," he said. "Following an exchange of fire with UN peacekeepers who were protecting the position, the base was partially looted. There were no casualties."
Who controls the Syrian side of 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 UN 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.
On Sunday, Prime Minister Netanyahu said Assad-linked Syrian troops had abandoned their positions on their side of the buffer zone. A UK-based war monitor also said troops left their posts in Quneitra.
Currently separating the Israeli and Syrian armies in the Golan is the Area of Separation, where UNDOF is stationed in camps and observation posts supported by military observers of the United Nations Truce Supervision Organization (UNTSO).
The 1974 disengagement agreement also 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 beyond the buffer zone 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 UN forces, a limited number of Druze civilians and for the transport of agricultural produce.
Who lives in Golan Heights?
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 estimated 31,000 Israelis have settled there, Mr Levine said. Many of them work in farming, including vineyards, and tourism.
ABC/Reuters
