Syrian troops have intensified their push for the country's last major rebel enclave — a "prelude to their total defeat," according to President Bashar Assad. The violence and mass displacement could result in the biggest humanitarian horror story of the 21st century, said the UN's humanitarian and emergency relief head, Mark Lowcock. Children in particular have become the face of this suffering.

Of the almost 900,000 forced from their homes and shelters in the last three months, 80% have been women and children, a UN spokesperson said. Around 300,000 of those have fled since the start of February alone. The wave of displacement is the largest exodus of civilians since World War II.

With temperatures reaching minus seven Celsius (19 degrees Fahrenheit) at the snow covered displacement camps in the hills near Turkey's borders, seven children have died from exposure and bad living conditions. Save the Children said families are burning whatever they can find to stay warm. The chairty warned the death toll could rise.

Convoys of Turkish commandos rolled toward the former "de-escalation zone" as Russian-backed Syrian forces intensified their push to retake the area in late January. After 13 Turkish soldiers stationed there to support rebels were killed in early February, diplomatic efforts to broker a cease-fire stalled.

Assad's offensive to retake the strategic M5 highway leading through Idlib province to Syria's second city, Aleppo; has been a long-term objective. After a Russian bombing campaign helped Syrian forces capture all towns along the route on February 11, fierce fighting in western Aleppo forced more than 43,000 toward the Turkish border.

The sheer number of Russian and Syrian aerial and artillery attacks on displacement camps, hospitals and schools "suggest they cannot all be accidental," UN human rights spokesperson Rupert Colville said. His office has recorded 299 civilian deaths this year, 93% caused by the Syrian government and its allies. Michelle Bachelet, the UN's human rights chief, called the campaign "indiscriminate."

Turkish-supported rebels have been caught out by the onslaught, as have jihadis who are not officially backed by Ankara. One Islamist group, Hayat Tahrir al-Sham, scored a rare victory last week when they downed a particular model of helicopter that Syrian forces are thought to use to drop barrel bombs on civilians.

The UN's Bachelet said "no shelter is now safe" and displacement camps have been overwhelmed by the number of those fleeing from the violence. Many have left the camps to take their chances on the road. Bachelet called for humanitarian corridors to be established to allow civilians to escape.

Turkey has closed its borders to prevent a further influx of Syrians. It already hosts 3.5 million refugees. That leaves the people of Idlib with no escape route. More than 500,000 of those fleeing are children.