The lives of more than 40,000 children are at risk amid the battle to recapture the ISIS stronghold of Raqqa in northern Syria, warned the United Nation’s children agency.

US-backed Syrian forces launched their attack on Raqqa earlier this week and US-led coalition airstrikes have intensified.

In a statement Friday, UNICEF said the violence has resulted in massive displacement in and around the city, with some 80,000 children now internally displaced and living in temporary shelters and camps.

“An estimated 40,000 children remain trapped in extremely dangerous conditions in Raqqa. Many are caught in the crossfire,” said UNICEF regional director Geert Cappelaere.

He called on all parties to provide safe passage to those wishing to leave the city.

US-led coalition forces launched heavy raids into Friday morning in support of Syrian fighters battling to oust ISIS from Raqqa, a monitor said.

The Kurdish-Arab alliance known as the Syrian Democratic Forces (SDF) broke into Raqqa city’s east earlier this week, months after they launched an operation to capture the extremist stronghold.

On Thursday night, the US-led coalition backing the SDF launched 25 air strikes on Raqqa city and its outskirts, the Syrian Observatory for Human Rights monitor said.

The Britain-based group reported 23 civilians killed in the overnight strikes, including 15 who were in an internet cafe in the western suburb of Jazra, just outside the city.

Observatory director Rami Abdel Rahman said heavy strikes continued on Friday morning as the coalition tried “to undermine ISIS capacity and open the way for the SDF to advance further in the city’s east and enter from other fronts”.

SDF spokesman Talal Sello said fighters were advancing against ISIS on several fronts.

“The SDF has control of Al-Meshleb district (inside eastern Raqqa) and is clearing it of mines and explosives at the moment,” he told AFP.

He said SDF forces were also advancing on the northern front outside the city, and had repelled an attack by the extremists as they pushed towards the city limits from the west.

Al-Meshleb was the first neighborhood in Raqqa city entered by SDF fighters.

They are expected to progress from the district into neighboring Al-Senaa and the Observatory said some of the overnight strikes targeted the area between the two districts.

ISIS extremists have been fighting back against the advancing forces with snipers as well as drones armed with explosives, according to the SDF.

They have also reportedly dug defensive trenches and tunnels to try to slow the SDF advance.

“Hundreds” of US military personnel are taking part in the Raqqa offensive, according to the Pentagon, which said Thursday it believed up to 2,500 extremists were still holed up in Raqqa.

An estimated 300,000 civilians were believed to have been living under ISIS rule in Raqqa, including 80,000 displaced from other parts of Syria.

But thousands have fled in recent months, and the UN humanitarian office estimates about 160,000 people remain in the city.