Syria's last major anti-government bastion, centred on the northwestern province of Idlib, was targeted by a deadly offensive by President Bashar al-Assad's forces late last year.
Here is some background about the hold-out area, where according to a UN investigation war crimes and possible crimes against humanity were committed.
- Bordering Turkey -
Idlib has a strategic location, sitting on the border with Turkey -- which has backed the rebel uprising -- and Latakia province, a regime stronghold on the Mediterranean coast and the heartland of Assad's clan.
Before war erupted in 2011, most of its population worked in agriculture, mainly growing cotton and cereals, or commuted to Aleppo, the country's second-largest city 60 kilometres (37 miles) away.
In March 2015 a coalition of Islamist fighters, including some linked to Al-Qaeda, seized the provincial capital Idlib, other key towns and government military installations.
- Jihadist 'government' -
In January 2018 fighting broke out in the area between Hayat Tahrir al-Sham (HTS), a jihadist group dominated by Syria's former Al-Qaeda affiliate, and more moderate rebels in the Turkey-backed National Liberation Front (NLF).
After making gains through combat or negotiated deals, HTS in January 2019 proclaimed administrative control of the area under a "Salvation Government".
The jihadist bastion now covers more than half of Idlib as well as adjacent parts of Hama, Aleppo and Latakia provinces.
- Idlib 'our goal' -
In 2017 Idlib was declared one of four de-escalation zones established by the three main foreign powerbrokers in Syria's conflict -- Turkey, Russia, and fellow regime ally Iran -- in a bid to reduce violence.
But late that year government forces backed by Russian air power launched an offensive on southeastern Idlib, which ended weeks later with their recapture of dozens of villages and towns there, as well as the military airport of Abu Duhur.
The government then retook the other three de-escalation areas -- Eastern Ghouta near Damascus, towns in Homs province, and Syria's south -- in military assaults culminating in surrender deals.
In July 2018 Assad said: "Now Idlib is our goal."
- Buffer zone and offensives -
In September 2018 Russia and Turkey announced a deal to create a 15- to 20-kilometre buffer zone separating rebel and regime fighters.
The accord held off any major regime assault but was only partially respected: the army maintained bombing raids and jihadist groups did not withdraw as required.
Between April and August 2019, Russian-backed offensives against Idlib by the Syrian army killed around 1,000 civilians, according to the Syrian Observatory for Human Rights war monitor.
More than 400,000 people were displaced, the UN said.
From December, despite a ceasefire announced at the end of August by Moscow, Russian-backed regime forces intensified their bombing raids. Violent fighting on the ground pitted them against rebels and jihadists.
Almost one million people fled the fighting between December and early March 2020, of whom around 780,000 are still displaced, according to the UN.
Nearly 500 civilians have been killed since December, according to the Observatory.
- Chemical attacks -
The government has been accused of staging several chemical attacks in Idlib, which it denies.
A UN commission found that helicopters from a pair of regime-controlled air bases dropped chlorine-filled barrel bombs on two Idlib villages in 2014 and 2015.
The commission later concluded the army also carried out a chemical attack, probably with chlorine, on a third village in 2015.
A sarin gas attack in April 2017 hit the town of Khan Sheikhun, killing more than 80 people, according to the Britain-based Observatory, which relies on a network of sources inside Syria.
The UN and the world's chemical weapons watchdog also said that sarin gas was used and that the regime, which denies the accusations, was responsible.
In April 2020, the watchdog published an official report in which it accused the Syrian army of chemical attacks in the northern area of Latamneh in 2017.