Aid agencies say a deal has been reached to send food and medicine into besieged towns in Syria, where tens of thousands of people are in danger of starving to death.

The aid deal agreed on Saturday will result in humanitarian supplies being sent to the opposition-held town of Madaya at the Lebanese border, and to two villages in the northwestern province of Idlib.

Aid agencies have warned of widespread starvation in Madaya, where some 40,000 people are at risk.

The UN said on Thursday that the regime had agreed to allow access to all three areas, but did not say when the delivery would take place.

"Both date and time have been set. Aid will go to three towns on Monday morning, all at the same time," said a source familiar with the matter. A second, pro-Syrian regime source confirmed the details.

Images of emaciated bodies and hungry children have led to an international outcry over the use of siege tactics by the regime.

News of the agreement came on Saturday as scores of people were killed and more than 100 others injured in Russian air strikes in Syria's Idlib province.

The volunteer-run Syria Civil Defense told Al Jazeera that Saturday's Russian air strikes targeted the town of Maarat al-Numaan, 290km north of the capital, killing at least 43 people and injuring at least 150 others.

"Our volunteers are still in the area that was targeted by the air strikes. They are still trying to help those injured and affected by the attack," the coordinator for the Idlib Syria Civil Defense told Al Jazeera.

"Many of those injured are in very serious conditions, the death toll is expected to rise," he added.

In another attack in Idlib province, the Syria Civil Defense said at least three people were killed and four others were injured in air strikes that targeted a school and a fire department in Ariha.

Known also as the White Helmets, the Syria Civil Defense is a group of volunteer rescuers formed in 2013 that now numbers more than 2,700 volunteers.

The UK-based Syrian Observatory for Human Rights put the death toll at 39, adding that the air strikes targeted a court and a prison in Maarat al-Numaan.

The Syrian Observatory said last week that more than 55,000 people, including almost 30,000 civilians, have been killed in Syria during the year 2015 alone.

PHOTO CAPTION

Residents help an injured man in a site hit by what activists said were airstrikes carried out by the Russian air force in the opposition-controlled area of Maaret al-Numan town in Idlib province, Syria January 9, 2016

Al-Jazeera