Thousands of civilians have fled areas in and around the Syrian city of Idlib in fear of a government counter attack after an alliance of rebel groups took over the provincial capital two days ago, the Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group, has said.

Rami Abdurrahman, the director of the SOHR, told Al Jazeera on Monday that the mass exodus occured amid widespread anticipation of devastating reprisals by the military after a coalition of seven armed factions, including Ahrar al-Sham and Nusra Front, seized the city on Saturday.

The "Fattah Army" alliance took control of the city, which is strategically located near the main highway connecting the the country's second city Aleppo and the capital Damascus, after five days of fierce clashes.

Damascus has reportedly sent one of its top military commanders, Suhail Al-Hassan, to lead an offensive that aims to recapture Idlib from the rebel fighters.

Al Jazeera's Suhaib al-Khalaf, reporting from Idlib, said that government forces have already launched deadly attacks on the city, destroying buildings and spreading fear of plans to carry out a major bombing campaign.

According to activists, at least 23 people, including children, were killed after troops carried out air strikes and shellings with surface-to-surface missiles targeting residential areas near the city's main hospital.

Al-Khalaf also reported that the military used chemical weapons in the bombardment, causing numerous victims to suffocate and seek medical care, without providing further details.

The Syrian Revolution Coordinators Union (SRCU), a nationwide activist group, has also accused the government of shelling Idlib city with explosives laden with chlorine gas.

Video posted on YouTube by activists claimed to show victims receiving treatment after showing symptoms of gas poisoning.

The government has been accused of killing hundreds of civilians with chemical weapons attacks on rebel-held areas across country. The government denies using chemical weapons.

Source: Al Jazeera