Five civilians died on Monday in Idlib as Syrian regime forces chip away at the country's last major rebel bastion, a war monitor said.
The Syrian Observatory for Human Rights said the deaths occurred in Jabal Al Zawiya, in the south of the rebel-dominated north-western stronghold of Idlib.
The monitor said from Britain that regime forces had rapidly gained ground in the southern part of Idlib in the past 24 hours.
They seized "several towns and villages" south of the M4 motorway linking the coastal regime stronghold of Latakia to government-held second city Aleppo, it said.
The fighting is coming "dangerously close" to encampments with about a million displaced people, risking an imminent "bloodbath", the UN said on Monday.
Mark Cutts, the UN's deputy humanitarian co-ordinator for the Syria crisis, said the UN was trying to double aid deliveries through a border crossing from Turkey to 100 lorries a day.
A months-long offensive by Syrian troops and their allies against rebels backed by Turkey in north-west Idlib has led hundreds of thousands of people to flee the violence.
As a result of the escalation, Mr Cutts said the UN was revising up its funding appeal for the crisis from $330 million (Dh1.21 billion) to $500m, and there was a shortfall of about $370m.
The UN sent 1,200 aid lorries into the area in January and 700 more so far in February, Mr Cutts said.
"The reality is, it is simply not enough," he said. "We're barely able to meet the needs of the people for the most urgent food rations and tents and blankets and winter items."
Mr Cutts said aid workers were "overwhelmed", some warehouses had been looted and fighting had damaged 77 hospitals and other medical centres.
State news agency Sana said "units of the Syrian army continued to progress in the south of Idlib" province.
Observatory chief Rami Abdulrahman said the regime's ultimate aim was to wrest back parts of the M4 still under control of the rebels.
That would require operations against the towns of Ariha and Jisr Al Shughour, which are both along the M4.
Analysts expect a tough battle for Jisr Al Shughour, held by the Turkestan Islamic Party whose fighters mainly hail from China's Uighur minority.
They are allied to Hayat Tahrir Al Sham, a group led by Syria's former Al Qaeda affiliate, which dominates the Idlib region.
In recent weeks, pro-Damascus forces have taken back control of another key commercial artery running through north-western Syria – the M5, which connects the capital with Aleppo.
They have also secured the region around the northern city, a major pre-war industrial centre.
Regime forces have since December clawed back large parts of the Idlib region, forcing close to a million people to flee their homes and shelters amid bitter cold.
Syria's war has killed more than 380,000 people and displaced millions since starting in 2011 with the brutal repression of anti-government protests.
