Syrian rebels have launched a surprise offensive in the country's north in a bid to capitalize on efforts by Israel, which has been targeting Iran's allies in the region for months.

After limited success in recent years, the rebels have now captured around 40 towns and villages controlled by government forces, as well as a Syrian military base.

Rebels have advanced on Aleppo, Syria's second-largest city, which has been under the control of the Assad government and pro-Iranian militias since 2016. Rebels say the offensive was launched to contain the Syrian government and " Iranian militia" which has "declared open war" against the Syrian people.

The surprise operation marks the first major conflict between Syrian rebels and the regime since March 2020, when Russia and Turkey brokered a ceasefire.

Over the past few months, Iran has seen its ally Hezbollah come under heavy Israeli air and ground attacks. The militant group, which was credited with helping to save the Assad regime from Syrian rebels, is now severely weakened and most of its leaders have been killed.

Opposition factions announced the offensive on their Telegram channel yesterday, calling it "preemptive aggression" and claiming it was in response to recent artillery bombardment by Syrian President Bashar al-Assad's regime in Idlib province.

A Turkish security source told CNN that rebels launched what was supposed to be a "limited operation" against Assad after the Syrian army and allied militia attacked the rebel-held city of Idlib, killing more than 30 civilians.

He added that the rebels expanded the operation after regime forces withdrew from towns around Aleppo. Iranian state media reported that Islamic Revolutionary Guard Corps General Kioumars Pourhashemi, Iran's top military adviser in Syria, was killed in Aleppo.

Russian and Syrian warplanes bombed rebel-held northwest Syria today to repel a rebel offensive. Analysts say the rebels are using the vacuum left by Hezbollah to advance in Syria.

"The rebels see an opportunity to test the front lines with Hezbollah weakened, Iran under pressure and Russia preoccupied with Ukraine... The rebels were surprised by their success and pushed harder than expected," said Nanar Hawach, analyst from the International Syria Crisis Group.

Hezbollah helped Assad regain territory, but its weakening came after Israel killed leader Hassan Nasrallah and many other senior officials of the pro-Iranian group.