Syrian and Russian jets are stepping up strikes on opposition forces in northern Syria in retaliation for the sudden offensive that has cost the regime control of the country’s second largest city, Aleppo.

At least 372 people have been killed since rebels launched a surprise offensive on Wednesday, according to observers.

The rebels’ success is a “direct consequence” of wars happening elsewhere, The Wall Street Journal wrote: al-Assad’s allies — Iran, Russia, and Hezbollah — are all embroiled in their own conflicts, and Turkey, which backs the rebels, took advantage.

Moreover, the offensive has come at a time when Syria’s biggest backers, Iran and Russia, have remained engaged in their own conflicts wherein Iran with Israel and Russia with Ukraine.

The surprise attack jolted the frontlines of the Syrian civil war that have largely been frozen since 2020. The army said it was preparing a counteroffensive.

Syrian armed opposition forces have entered Aleppo just three days into their surprise offensive, marking the first time they have set foot in the country’s second largest city since government forces recaptured the city in 2016.

NBC News’ Matt Bradley reports on the intensifying violence in the Syrian rebel offensive after Russian and Syrian jets struck a rebel held city in the northern part of the country. Syrian President Bashar Assad is vowed to crush insurgents waging a shock offensive against his regime.

Russian and Syrian warplanes targeted insurgents in an Aleppo city suburb on Saturday, two Syrian military sources said, after the rebel fighters penetrated the heart of the city in Syria's northwest in a surprise attack the previous day.

Russia's Defence Ministry said its air force had carried out strikes on Syrian rebels in support of the country's army, Russian news agencies reported on Saturday, amid an advance by forces opposed to Syrian President Bashar al-Assad.