Syrian and Russian forces carried out the most intense bombing in weeks on Idlib province on Saturday, raising fears of an imminent assault on the densely populated rebel-held area.
The renewed strikes came a day after Syrian regime allies Russia and Iran, and Turkey, a supporter of Syrian rebel factions, disagreed on the fate of the province at a summit in Tehran. Russia and Iran backed a military offensive to reclaim the last major rebel-held area of Syria, while Turkey called for a ceasefire to prevent mass casualties among the province's estimated 3.5 million population.
The Syrian Observatory for Human Rights monitoring group said dozens of Russian air raids hit southern and south-eastern areas of Idlib on Saturday. At least four civilians, including two children, were killed in the strikes and as dozens of barrel bombs were dropped by regime aircraft, the Britain-based monitor said.
Observatory head Rami Abdel Rahman said it was the heaviest bombardment since August 10, when at least 53 civilians were killed in Idlib and neighbouring province Aleppo.
He said the strikes targeted positions of both rebel groups and the rival Hayat Tahrir Al Sham alliance, led by Al Qaeda's former Syrian affiliate and comprised mostly of hard-line Islamist groups.
The United Nations has said an offensive on Idlib could force as many as 800,000 civilians to flee their homes and has urged world powers to prevent a "bloodbath".
Many of Idlib's residents have already fled fighting in other areas of the country during Syria's seven-year civil war.
Syrian state media said the attacks on Saturday were a retaliation to overnight shelling from rebel-held areas on a government-held town in Hama province, south of Idlib, that killed nine civilians.
Russian jets had struck Idlib on Friday, before the talks in Tehran between Turkish President Recep Tayyip Erdogan, Russian President Vladimir Putin and Iranian President Hassan Rouhani.
Mr Erdogan called for a "truce" at a press conference after the talks.
“Any attack on Idlib would result in a catastrophe. Any fight against terrorists requires methods based on time and patience. We don’t want Idlib to turn into a bloodbath,” he said.
Mr Putin said Damascus "has a right and must eventually take under control all of its national territory", while Mr Rouhani warned against a "scorched earth" policy, but said "fighting terrorism in Idlib is an unavoidable part of the mission".
Nicholas Heras, a researcher at the Centre for New American Security, said the spike in Russian raids on Saturday aimed to put pressure on Turkey to agree to a deal for a regime takeover of Idlib.
"Russia is reminding Turkey it needs to stay in Russia's good graces if Turkey wants to avoid a painful catastrophe in north-west Syria," Mr Heras told Agence France-Presse.
Russian military spokesman Igor Konashenkov, meanwhile, said Moscow had "irrefutable information" that Syrian rebels were planning a "provocation" in Idlib province to justify western intervention.
The United States has about 2,000 troops in other areas of Syria, but little leverage in Idlib, which had been declared a "de-escalation" zone under an agreement reached a year ago between Russia, Turkey and Iran. Turkey has troops stationed in Idlib and 12 observations posts around the province as part of the pact.
US Ambassador to the UN Nikki Haley warned on Friday of dire consequences if Idlib was attacked.
Speaking at the Security Council, Mrs Haly said the US considered an assault on Idlib to be "a dangerous escalation of the conflict in Syria”.
“If Assad, Russia and Iran continue, the consequences will be dire,” she said.
“We urge Russia to consider its options carefully. Stop Assad’s assault on Idlib. Work with us and the UN to find peace at last for Syria.”
UK Ambassador to the UN Karen Pierce said: There are more babies in Idlib than terrorists. UN estimates that terrorist fighters make up just 0.5 per cent of population, but three million civilians are at risk."
"We call on Russia to do more to restrain the Syrian regime from attacking, and avert humanitarian catastrophe," she added.
Separately, clashes broke out in eastern Syria in Qamishli, a town close to the border with Turkey, between government and Kurdish security members. The Syrian Observatory for Human Rights said the clashes left 10 government security personnel and seven Kurdish fighters dead.
The town is run by Kurdish-led administrators and forces, but Syrian government troops hold pockets of territory there, including the airport. Occasional clashes have erupted over turf control and authority, reflecting deepening political tensions between the uneasy partners.
Kurdish security forces, known as Asayish, said that a government patrol entered the areas controlled by the Kurdish militia in Qamishli and began arresting civilians, then shot at a Kurdish checkpoint, sparking the gun battle. The Asayish said seven of its members and 11 government personnel were killed.
Journalist and local resident Arin Sheikmos told Associated Press the government security troops carried out an arrest campaign in Kurdish-controlled areas, detaining people it accused of dodging military conscription. This prompted the clashes that lasted no more than 20 minutes, he said.
There was no immediate comment on the clashes by the government.
The US-backed Kurdish administration has recently begun talking with the Syrian government, seeking government recognition of its self-rule areas. But in recent days, the Damascus government announced that it will be holding local administration elections, including in Kurdish-ruled areas, undermining the negotiations with the Kurds and their proposal for self-rule.
The Kurdish-led administration control nearly 30 per cent of Syria, mostly in the north-eastern part of the country, including some of Syria's largest oilfields. They seized the territories, with the backing of the US-led coalition, after driving out ISIS militants.