The Syrian regime and its ally Russia have for three months ramped up bombardment of the last major jihadist-run bastion in the country after eight years of brutal conflict.
The strikes pummelling the northwestern Idlib region have claimed more than 730 lives since late April, according to the Britain-based Syrian Observatory for Human Rights war monitor.
The UN says more than 400,000 people have been displaced.
The region was meant to be protected from a regime assault by a September 2018 buffer zone deal, signed by Damascus ally Russia and rebel backer Turkey.
Here is some background.
- Jihadist stronghold -
Regime and Russian strikes pick up after the powerful Hayat Tahrir al-Sham (HTS) jihadist alliance, led by Syria's former Al-Qaeda affiliate, takes control of the area in January 2019.
A major escalation begins in late April, after clashes and strikes since February had already killed around 200 civilians, according to the UN.
Bordering Turkey, the region under HTS control covers nearly all of Idlib province and parts of neighbouring Aleppo, Hama and Latakia provinces.
It is home to some three million people, nearly half already displaced from other regions during Syria's war.
- Escalation -
On April 26, Russia and the regime's other main ally Iran pledge along with rebel backer Turkey to cooperate to "ultimately eliminate" HTS.
After Russian raids on April 26-27 kill around 15 civilians, the UN warns Moscow to abide by its commitment to "avoid large-scale military offensives" on the region.
Russia denies targeting civilians.
- 'Humanitarian disaster' -
By early May the strikes have forced 150,000 people to flee and knocked 12 hospitals and 10 schools out of action, the UN says.
Britain, France, the United States and eight other countries at the UN Security Council warn on May 10 of a "potential humanitarian catastrophe".
On May 17, Amnesty International accuses the regime and Russia of a "deliberate and systematic assault" on hospitals.
- Banned weapons -
The US says on May 22 there are indications the Syrian government used chemical weapons in Idlib. France says it has similar information. Neither offer up proof.
On June 3, Human Rights Watch accuses the regime and Russia of using "internationally banned" weapons in attacks on civilians.
They include cluster munitions and large air-dropped "barrel bombs", it says.
- No let up -
On May 22, regime air strikes kill 23 civilians, most of them at a market in Maaret al-Numan, according to the Observatory.
Dozens more die in days of bombardment over the last week in May.
A new flare-up kicks off on June 15 when at least 45 people, including 10 civilians, are killed in clashes as regime forces push to retake two villages seized by jihadists and allied rebels earlier in the month.
Regime bombardment on June 20 kills 20 civilians including eight children and three rescue workers.
Strikes on July 21 kill 18 civilians including young citizen journalist Anas al-Dyab, who was a member of the White Helmets rescue group and also contributed to AFP.
The following day, regime and Russian air strikes kill 50 people at a vegetable market in Maaret al-Numan.
On July 26, UN human rights chief Michelle Bachelet condemns "international indifference" in the face of the mounting death toll, and warns that those responsible could be charged with war crimes.
