Russia and China have vetoed a United Nations Security Council resolution that called for a truce in the region of Idlib, the last rebel-held stronghold in northwestern Syria, Al Jazeera reports.

The resolution said, "All parties shall immediately cease hostilities to avoid a further deterioration of the already catastrophic humanitarian situation in Idlib Governorate, beginning at noon Damascus time on 21 September 2019."

Russia vetoed the call for action because it did not include an exemption for military offensives against the UN-blacklisted fighter groups.

It was the 13th time Russia vetoed a resolution on the Syrian conflict and the seventh in the case of China.

Equatorial Guinea abstained, while the remaining 12 members of the council voted in favour of the resolution, which was drafted by Kuwait, Belgium and Germany.

"As co-penholders of the humanitarian file for Syria in the Council, we would like to call upon all member states to vote in favor of our resolution," the three drafters said.

"Our draft resolution the Council will vote on today is a purely humanitarian one," they said, noting that half a million people have been displaced since the Idlib offensive began four months ago.