Russian air strikes killed at least 23 civilians Tuesday in northwestern Syria, as renewed violence tightened the noose around the country's last major rebel-held bastion and deepened an already dire humanitarian crisis.

Retaliatory rocket attacks blamed on rebels and jihadists killed three more civilians in the nearby government-held city of Aleppo, state news agency SANA said. The spike in violence in the neighbouring provinces of Aleppo and Idlib follow so far unsuccessful diplomatic attempts to reduce hostilities in the flashpoint region, with the latest truce in theory going into effect less than two weeks ago.

Most of Idlib and parts of Aleppo province are still controlled by factions opposed to President Bashar al-Assad's regime, including a group that includes onetime members of Al-Qaeda's former Syria franchise.

The Damascus regime, which controls around 70 percent of the country after nearly nine years of war, has repeatedly vowed to recapture the region.