Iran’s foreign minister, Abbas Araghchi, says he will leave Tehran for Damascus today to deliver a message of support for Syria’s government and armed forces.

“I am going to Damascus to convey the message of the Islamic Republic to the Syrian government,” Araghchi said, emphasising Tehran will “firmly support the Syrian government and army,” the Irna state news agency reported. Araghchi will then make a diplomatic visit to Turkey, which backs rebel groups along Syria’s northern border but has sought recently to normalise relations with Assad.

The Syrian army said on Saturday that dozens of its soldiers had been killed in a major attack led by Islamist Hayat Tahrir al-Sham rebels who swept into the city of Aleppo.

In a phone call with his Russian counterpart, Sergei Lavrov, yesterday, Araqchi said that the attacks were part of an Israeli-US plan to destabilise the region, state media said.

Welcome to our live coverage of the surprise offensive by rebels in Syria. We will be providiing you with the latest updates throughout the day.

Opposition fighters are now reported to have taken control of Aleppo, Syria’s second largest city, and have pushed into several towns in the countryside near the country’s fourth largest city, Hama.

Islamist-led rebels on Saturday seized Aleppo’s airport and dozens of nearby towns after overrunning most of Aleppo, a war monitor said.

Syria’s army confirmed that the rebels had entered “large parts” of the city of around two million people and said “dozens of men from our armed forces were killed”.

On Wednesday, the jihadist group Hayat Tahrir al-Sham (HTS) and allied factions launched a surprise attack on government-held areas of northern Aleppo province, triggering the fiercest fighting in years, the Syrian Observatory for Human Rights said (SOHR).

More than 300 people, including at least 20 civilians, have been killed since Wednesday, according to the British-based war monitor.

President Bashar al-Assad, whose regime is backed by Moscow and Tehran, has vowed to “defend [Syria’s] stability and territorial integrity in the face of all terrorists and their backers”.

As my colleague Ruth Michaelson notes in this story, the surprise offensive in which insurgents seized territory across north-western Syria marks the most serious challenge to Assad’s control in years. Syria has been gripped by civil war for more than a decade, although the intensity of the conflict had decreased in recent years.

At least one civilian was killed after Russia carried out five consecutive airstrikes targeting a refugee camp in a neighbourhood in Idlib, according to the SOHR.

It said earlier today that Russia targeted rural parts of Idlib and Hama where the group leading the rebel offensive “has recently taken control”. The Idlib region is subject to a ceasefire – repeatedly violated but which had largely been holding – brokered by Turkey and Russia after a Syrian government offensive in March 2020.