Rebels led by the Islamist militant group Hayat Tahrir al-Sham launched an incursion on Wednesday into a dozen towns and villages in the northwestern province of Aleppo, which is controlled by Syrian President Bashar al-Assad's government.
The Syrian military said it continued to confront the attack, saying in a statement it had inflicted heavy losses on the insurgents in the countryside of Aleppo and Idlib.
The militants reportedly entered some areas inside Syria's second-largest city Aleppo, according to activists and rebels.
"The rebels have entered areas inside the city of Aleppo for the first time since 2016," Rami Abdel Rahman, head of the opposition Syrian Observatory for Human Rights, said.
"Our forces have begun entering the city of Aleppo," a statement from a newly formed rebel coalition said.
Kremlin spokesman Dmitry Peskov said Russia, which has forces in Syria backing Assad, regarded the rebel attack as a violation of Syria's sovereignty and wanted the authorities to act fast to regain control.
The attack was the biggest since March 2020 when Russia and Turkey, which supports some of the rebels in the northwest, agreed to a deal that de-escalated the conflict.
David Carden, UN Deputy Regional Humanitarian Coordinator for the Syria Crisis, said: "We're deeply alarmed by the situation unfolding in northwest Syria."
"Relentless attacks over the past three days have claimed the lives of at least 27 civilians, including children as young as eight years old," he told Reuters.
"Civilians and civilian infrastructure are not targets and must be protected under international humanitarian law."
Syrian state news agency SANA said four civilians including two students were killed on Friday in Aleppo by insurgent shelling of university student dormitories.
It was not clear if they were among the 27 dead reported by the UN official.
Russian and Syrian warplanes bombed the area near the border with Turkey on Thursday to try to push back an insurgent offensive that has captured territory for the first time in years, Syrian army and rebel sources said.
Asked about unconfirmed Russian Telegram reports that Assad had flown into Moscow for talks with Russian President Vladimir Putin, Peskov said he had "nothing to say" on the matter.
with DPA
