Thousands of people have been displaced and dozens killed in one of the worst flare-ups to rattle a precarious truce deal in north-western Syria, AFP reported Tuesday (February 26th).

Attacks by an extremist group on the edge of Idlib province have killed 20 regime and allied fighters since Sunday, the Syrian Observatory for Human Rights said.

The latest casualties were five regime and allied fighters killed Tuesday near a planned buffer zone around opposition-held territory in Idlib.

The Observatory said the attack was led by al-Qaeda affiliate Hurras al-Din.

At least nine extremists were killed in the clashes, among the deadliest since a deal was reached in September to spare the region a massive regime assault.

Regime bombardment near Khan Sheikhun, in Idlib province, also killed two civilians on Tuesday, raising the civilian death toll to 42 since February 9th, the Observatory said.

"The UN remains deeply concerned for the safety and protection of thousands of people recently displaced from Khan Sheikhun following an increase in hostilities in the area," said David Swanson, spokesman for the UN Regional Office for the Syria Crisis in Amman.

He said 7,033 women, children and men were displaced from Khan Sheikhun between February 1st and 21st.

The vast majority moved to districts within Idlib, while around 152 people were displaced to the town of Afrin in Aleppo province.