UN Syria envoy Staffan de Mistura said the anticipated battle in Idlib would affect millions of civilians.

Air raids have pounded areas in Syria’s last rebel-held province of Idlib, killing several civilians and raising further concerns that an all-out government offensive is only a matter of time.

At least 24 raids – the first in three weeks – hit the area on Tuesday.

Idlib would be “the perfect storm”, said UN Syria envoy Staffan de Mistura earlier this week. A battle, he said, would affect millions of civilians and could see both sides use chemical weapons.

Similarly, Filippo Grandi, the head of the UN’s refugee agency, cautioned that a wider offensive would cause renewed displacement while exacerbating an already dire humanitarian situation.

The attacks on Tuesday came as the United Nations urged Russia, a Syrian government ally, and Turkey, which backs certain rebel groups in Idlib, to help avert a “bloodbath”.

There are an estimated 70,000 rebel fighters in and around the province. Idlib is strategically important as on one side it shares a border with the province of Latakia, home to the biggest Russian naval and airbase in Syria, and on the other side, it borders Turkey.

The strategic M5 highway – the main access road to the north – also passes through Idlib.

The bombing mainly targeted the city of Jisr al-Shughour on Idlib’s western edge, along with its surrounding towns and villages, activists told Al Jazeera.

The attacks lasted for several hours before subsiding at around 7pm local time (17:00 GMT).