Syria war: Why does the battle for Idlib matter?
The opposition-held province of Idlib in north-western Syria could become the scene of the final, and perhaps bloodiest, showdown between the government and armed groups seeking its overthrow. The UN says the result could be a humanitarian catastrophe.
What's so important about Idlib?
The province, along with adjoining parts of northern Hama and western Aleppo, is the last stronghold of the rebel and jihadist groups that have been trying to overthrow President Bashar al-Assad for the past eight years.
The UN estimates it is home to 3 million people, including 1 million children. More than 40% of the civilians there come from other previously opposition-held areas.
Idlib also borders Turkey, to the north, and straddles highways running south from Aleppo to Hama and the capital Damascus, and west to Latakia on the Mediterranean coast - all cities controlled by the government.
If Idlib is retaken by Mr Assad, it would effectively signal the opposition's defeat.
Who controls the province?
Idlib had been controlled by a number of rival factions, rather than a single group, since it fell to the opposition in 2015. But in January 2019 the jihadist alliance Hayat Tahrir al-Sham (HTS) staged a violent takeover.
It expelled some mainstream rebel fighters from Idlib to the neighbouring Afrin region, which is controlled by Turkish-backed factions, and forced those remaining to accept civilian control by an administration it backs - the "Salvation Government".
HTS, which was known as al-Nusra Front before it broke off formal ties with al-Qaeda three years, is designated as a terrorist organisation by the UN.
Estimates put the number of opposition fighters currently in Idlib, Hama and Aleppo at between 20,000 and 50,000. It is not clear how many are jihadists.
In January, a UN committee cited a member state as saying HTS had some 20,000 fighters in Idlib province, including a significant number of foreigners.
The Turkistan Islamic Party, a mostly Chinese Uighur group closely allied to HTS, is also estimated to have a few thousand fighters. Hurras al-Din, which is widely believed to be al-Qaeda's new Syrian branch, and the rival Islamic State (IS) group are thought to have several hundred fighters each.
Before the HTS takeover, most non-jihadist groups in Idlib fought under the banner of the Turkish-backed National Liberation Front (NLF). NLF factions that stayed neutral, like Faylaq al-Sham, or yielded to HTS, such as Ahrar al-Sham and Suqour al-Sham, continue to operate on the ground.
Why has the government stepped up its attacks?
The civil war has swung heavily in President Assad's favour in the past three years. Air strikes by his ally, Russia, and support from thousands of militia fighters backed by Iran, his other main ally, have helped the Syrian army recapture opposition strongholds elsewhere in the country.
In August 2018, the government declared that its priority was to "liberate" Idlib and troops prepared for an all-out assault.
But the following month, the presidents of Russia and Turkey averted an offensive by agreeing to establish a "demilitarised buffer zone" along the front line. Mainstream rebels were required to pull their heavy weapons out of the zone, and jihadists were told to withdraw altogether.
Turkish troops were deployed to monitor the agreement, but it was never fully implemented. Rebels reportedly withdrew some heavy weapons, but the jihadists stayed.
Since the HTS takeover there has been a marked escalation in hostilities. Government and Russian air strikes have pounded the opposition enclave, while jihadists have shelled government-held areas.
The UK-based Syrian Observatory for Human Rights monitoring group says that since mid-February at least 615 civilians and 483 rebel and jihadist fighters have been killed attacks by the government and its allies.
In the same period, opposition attacks have killed 50 civilians and 437 troops and pro-government militiamen, according to the SOHR. More than 1,000 of the fatalities - a third of them civilians - have been reported since 30 April, when government forces began advancing from the south.
The government has said it is responding to violations of the truce agreement and that it will "spare no effort to rescue its citizens from the dominance of terrorist organisations in Idlib".
HTS leader Abu Mohammad al-Jawlani has said his group will "keep fighting until the last breath for every inch of land we control".
What could happen to the civilians in Idlib?
UN Secretary General António Guterres stressed in September that it was "absolutely essential to avoid a full-scale battle in Idlib", warning such a scenario would "unleash a humanitarian nightmare unlike any we have seen" in Syria.
Many displaced people are already experiencing dire conditions in overcrowded sites where basic services are stretched to breaking point. Two-thirds of the 270,000 people displaced by the latest fighting are reportedly living in open fields or sheltering under trees.
The UN and its humanitarian partners have already been forced to suspend operations in areas of active hostilities, and they have said a full government incursion would "overwhelm all ability to respond".
To compound matters, the millions living in Idlib seemingly have nowhere else to go. Turkey's border is closed, the Afrin region is already crowded with displaced people, and many opposition supporters fear imprisonment if they cross into government territory.
UN Emergency Relief Co-ordinator Mark Lowcock has said a failure to end the violence and find a long-term solution could result in "the loss of huge numbers of people - running into hundreds of thousands, possible even more".
Can an attack on Idlib be prevented?
That appears to depend on Turkey and Russia.
Turkey, which is already home to three million Syrian refugees and fears a new wave of people heading towards its border, has accused the Syrian government of breaching the truce and told Russia that its ally "must be controlled".
But Russia has said it is the "responsibility of the Turkish side" to first put an end to attacks by jihadists on civilians and Russian military positions.
Russian President Vladimir Putin has refused to rule out a full-scale assault on Idlib, but he has also noted that "we and our Syrian friends consider that to be inadvisable" because of the humanitarian situation.