The impact of the military offensive in Idlib may be the worst it has seen in Syria, the UN said Thursday.

In a statement, UN Special Adviser on the Prevention of Genocide Adama Dieng urged all the parties in the conflict in Syria to protect civilians in accordance with international law.

"Time and again we have witnessed the horrors faced by the civilian population in Syria - in Aleppo, in Eastern Ghouta, in Raqqah, and most recently in Dara’a and Qunaitra. Given the high population of civilians in Idlib, the impact of a military offensive there may be the worst we have seen in Syria yet,” Dieng said.

The special envoy expressed support for the call by the Special Envoy to Syria Stephan de Mistura for a political solution to the conflict.

Dieng noted Idlib is the last de-escalation zone under the Astana agreement of May 2017, and holds hundreds of thousands of civilians that have sought refuge there.

An estimated 2.9 million people are living in the area, including 1 million children. Half of these people were displaced from other parts of the country, according to Dieng.

Located near the Turkish border, Idlib is home to more than 3 million Syrians, many of whom fled from other cities following attacks by regime forces.

The Syrian regime has recently announced plans to launch a major military offensive to the area, which is controlled by various armed opposition groups.

Russian warplanes on Tuesday pounded civilian and opposition targets in Idlib.

On Tuesday, the UN’s humanitarian chief Mark Lowcock warned that such an offensive would lead to the "worst humanitarian catastrophe in the 21st century".

"A military offensive in Idlib could be catastrophic for the civilians who have sought protection there. Previous Government offensives in areas controlled by armed opposition groups in Syria have been carried out with little regard for the lives of civilians," Dieng said.