BEIRUT - Syrian regime airstrikes and artillery fire killed 23 civilians on Sunday across the rebel-held Eastern Ghouta region outside the capital Damascus, a monitor said. The deaths come despite the area falling within a so-called "de-escalation zone" put in place under a deal between government allies Russia and Iran and rebel backer Turkey.

Eastern Ghouta is already in the grip of a humanitarian crisis caused by a crushing regime siege of the area since 2013 that has caused severe food and medical shortages. Meanwhile, Russian airstrikes killed 34 civilians , among them 15 children, in a village held by the Islamic State group in Syria 's eastern Deir Ezzor province, a monitor said. The Britain-based Syrian Observatory for Human Rights said the strikes hit the village of Al-Shafah, on the eastern bank of the Euphrates River, in the early hours of Sunday morning.

On Sunday, government air strikes on the areas of Mesraba and Madira killed 21 civilians , while artillery fire on the town of Douma killed another two civilians , the Britain-based Syrian Observatory for Human Rights monitor said. "The toll could rise further because of the number of wounded people in a serious condition," said Observatory director Rami Abdel Rahman.

Among the dead were four children, the Observatory said. Regime bombardment of Eastern Ghouta in the last two weeks has killed more than 100 people, according to the Observatory. Rebels have also fired from the region into Damascus, killing several people.

Humanitarian access to Eastern Ghouta has remained limited despite the implementation of the truce zone, and a United Nations official referred to the region as the "epicentre of suffering" in Syria . More than 340,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests. The Observatory relies on a network of sources inside Syria , and says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.

Russia is a close ally of Syria 's President Bashar al-Assad, and in September 2015 began a military intervention in support of his government that has gradually helped Damascus regain territory.

Syria 's Deir Ezzor is one of the last places IS jihadists hold territory in the country, after being driven from their major strongholds including their one-time de facto Syrian capital Raqa city.

The oil-rich eastern province that borders Iraq was once almost completely under IS control, but the jihadists now hold just nine percent of Deir Ezzor, according to the Observatory.

They have faced two separate offensives there, one led by the regime with Russian backing and the other by the US-backed Syrian Democratic Forces, an alliance of Kurdish and Arab fighters.