Camps for the displaced are overstretched, forcing many to seek shelter in some 160 makeshift settlements in Idlib, assistant-secretary general for humanitarian affairs Ursula Mueller told the Security Council.
"During these cold and wet winter months, many families have nothing else than improvised tents which they share with others," she said.
With Russian military backing, Syrian troops launched an offensive in late 2017 against jihadists and allied groups in Idlib, the last province still fully outside the government's control in the nearly seven-year war.
"Airstrikes and fighting in southern Idlib and northern Hama have resulted in over 270,000 displacements since December 15," said Mueller.
At least 16 hospitals and clinics were attacked in Idlib last month alone, she added.
Further north, in the Afrin area, some 15,000 people have been displaced within the district and another 1,000 have fled to neighboring Aleppo governorate, said Mueller.
Turkey launched air strikes and shelling on the border region on January 20, targeting the Kurdish YPG militia that it considers a terror group.
Mueller told the council that Syria had blocked all aid convoys to besieged areas in January after allowing only two relief shipments to reach hard-to-reach areas last month.
Access to other parts of Syria are being hampered, with local authorities requesting changes to aid operations in the northeast, she said.
The new hurdles in deliveries of food and medical supplies came after UN aid chief Mark Lowcock visited Syria earlier this month.
More than 13.1 million Syrians are in need of humanitarian aid including 6.1 million who have been displaced within the country.
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