Ankara will not tolerate any delay from the US over setting up a safe zone in northern Syria, Turkey's foreign minister said on Thursday.

Still reeling from his sudden deportation from Turkey with just the clothes on his back, Mohammad Hassan stood in the arrivals hall at a border crossing in northern Syria unsure what to do next.

More than 400,000 people have been displaced in northwestern Syria over the past three months, the UN said Friday, as the government presses an intensified bombardment of the rebel-held region.

Maha al-Nasser queues in front of a crowded clinic in Syria's Al-Hol camp, her frail daughter squirming in her arms under the stifling desert heat.

"My daughter has suffered from convulsions and malnutrition," said 30-year-old Nasser, her face covered in a black veil.

Russia on Thursday opposed a United Nations Security Council resolution calling for an end to attacks on health facilities in Syria's Idlib region, diplomats said after the latest meeting over violence in the country's last major opposition bastion.

A blast killed four soldiers in southern Syria Wednesday in a rare such deadly attack in the defeated cradle of the eight-year uprising, a war monitor said.

Two months of intensive airstrikes by Syrian government forces and their Russian allies, coupled with a fierce ground assault on rebel-controlled Idlib province, have killed hundreds of people and caused massive displacement while achieving little to no gain for President Bashar Assad.

Despite the heavy bombardment, Assad's troops have been unable to make any significant advances against al-Qaida-linked militants and other jihadi groups who dominate Idlib province, the last significant area held by opposition forces. Militant attacks have killed an average of more than a dozen soldiers and allied militiamen a day in recent weeks.

At least 10 civilians were killed Friday in Syrian regime air strikes in the country's northwest, including three children, a war monitor said.

UN Secretary General Antonio Guterres on Thursday strongly condemned air strikes in northwest Syria following reports that four health facilities were hit during a single day of bombing.

Syria's eight-year war has seen the Damascus regime lose control of key oil fields and caused state hydrocarbon revenues to plummet by billions of dollars.