More than 235,000 civilians have fled their homes in opposition-held areas of north-west Syria in the past two weeks, the UN has said, after attacks by Syrian government forces intensified.

Syrian troops and their foreign backers are targeting the towns of Maaret al-Numan and Saraqeb in Idlib province, which sit on a highway connecting Aleppo with the capital, Damascus.

The attacks come in defiance of an August ceasefire deal and calls for de-escalation from Turkey, France and the UN. Bashar al-Assad’s government, which controls 70% of Syria, has repeatedly vowed to take back Idlib.

There are an estimated 3 million civilians living in the province, including many who had already fled violence in other parts of Syria during the country’s long civil war.

A wave of aerial bombing began around 16 December, followed by a ground offensive from 19 December, a statement from the UN Office for the Coordination of Humanitarian Affairs said.

Kana’an al-Ahmad, a field commander with the National Front for Liberation (NFL), said: “The regime is trying to besiege the city of Maaret al-Numan from three sides but we are still repelling it.

“We were planning to launch a counterattack but the weather conditions didn’t help us so our plan was cancelled. But we are preparing for another in the coming days. Many reinforcements from other rebel groups have also arrived to fight alongside us.”

He said the fighters were hindered by their limited equipment. “Because regime is using modern tanks, we can’t destroy them with the old missiles we own.” He claimed both sides had sustained heavy losses.

A camp for displaced Syrians at Khirbet al-Jouz in the west of Idlib province near the border with Turkey. Photograph: Aaref Watad/AFP/Getty Images

Much of the area is dominated by the country’s former al-Qaida affiliate, Hayat Tahrir al-Sham, whose leader this week urged jihadists and allied rebels to head to the frontlines and fight the “Russian occupiers” and the government.

The scale of the December exodus prompted Donald Trump to call for a halt to the fighting in a tweet from his Mar-a-Lago resort. “Russia, Syria and Iran are killing, or on their way to killing, thousands of innocent civilians in Idlib province. Don’t do it! Turkey is working hard to stop this carnage,” he wrote.

With the Turkish border closed, aid groups are warning of a humanitarian crisis as waves of displaced families are pushed into ever-shrinking rebel territory.

“The capacity to absorb people in need may surpass available places given the scale of displacement,” the UN said. “Many of those who are displaced as a result of the most recent intensification of hostilities had been displaced previously, some of them multiple times.”

Even inside Idlib, the UN estimates that a previous wave of attacks displaced around 400,000 people between April and August. The areas targeted in the latest offensive are said to be almost empty.

“I left the city three days ago. The sky was raining bombs and rockets,” said Omar Basher, 25, from Maaret al-Numan, who worked for a local charity until it closed around a year ago.

“I never thought I would leave my home forever, but now as the regime is advancing and it’s getting closer to the city, I have the feeling that I will never go back.

“I am with my parents and my two brothers and are still trying to find a house, but everywhere the houses are already full of displaced. We might go to Turkey although the borders are closed and it’s pretty dangerous to try to cross the borders.”

In al-Atarib, in the countryside west of Aleppo, residents have organised a scheme to support the latest wave of people fleeing violence, called “be generous with them”, funded by donations from the community.

“Someone from the town donated farmland to set up tents for the displaced, many people donated money, clothes, blankets, mattresses, foodstuff and bed covers, also we made makeshift toilets for them,” said Ali Obeid, a spokesperson for the group.

“We are still receiving new arrivals, we had 20 families yesterday but today we have 50 families. So we are trying to get more tents and plastic sheeting to protect from the rain. We have also secured batteries and LEDs to light their tents.”

Obeid said one of the biggest concerns was that the camp would be bombed. “The regime and Russia have done this many times in many areas,” he said.

Attacks on the area have repeatedly targeted civilian infrastructure including markets and medical facilities. The Syrian American medical society said 71 hospitals or clinics had been hit between April and December.

Unicef said children were bearing the brunt of the intensifying violence, with at least 65 killed or injured in December. By the end of the month nearly 50,000 were in urgent need of education support, excluded from school by violence and displacement.