Syrian opposition fighters have blown up bridges linking rebel-held territories to government-controlled areas in anticipation of a military offensive to take their last stronghold.
The move in the northwest of Syria comes as the United Nation’s high commissioner for refugees, Filippo Grandi, warned a potential government offensive could cause further displacement and discourage other refugees from returning home.
Explosions south of Idlib, in the al Ghab plains, came after opposition forces detected the movement of government troops in the area, according to the head of the Syrian Observatory for Human Rights, Rami Abdurrahman.
He said two other bridges remained in the area and could be used by state forces to recapture the opposition stronghold.
Most of Idlib and the adjacent area of Hama remain under the control of several different armed groups – some which are backed by Turkey, others by independent Islamist groups.
However, the strongest set of fighters is led by an al Qaeda-linked group, which controls most of an area that is home to more than three million people.
In response, thousands of state troops and allied fighters have been surrounding the areas around Idlib.
Syria’s key ally, Russia, said a military operation was needed to flush out “terrorists” from the area, which have been blamed for targeting coastal army bases.
Sergey Lavrov, Russia’s foreign minister, said talks were under way to establish a humanitarian corridor for civilians to leave Idlib.
Turkey has aired fears of a potential humanitarian crisis on its borders. The country, which backs several opposition groups in Syria, has set up observation point around the rebel stronghold and has been seeking to stop a full-scale state offensive.
About 800,000 people are at risk of being displaced if the military action went ahead, according to UN officials. Almost two million people in the area have already been displaced from other parts of Syria.
As well as blowing up bridges, the rebel forces have dug trenches and built berms in preparation.
Al Qaeda-linked authorities have also called on people living in the stronghold to support fighters by building reinforcements or volunteering to fight.
Thousands of protesters in several towns in Idlib and Hama rallied against an offensive and in support of the rebel fighters.
Idlib remains the last major territory for the Syrian government to secure after seven years of a deadly civil war.