Syria's eight-year war has seen the Damascus regime lose control of key oil fields and caused state hydrocarbon revenues to plummet by billions of dollars.

A supertanker suspected of carrying crude oil to Syria in violation of EU sanctions was detained in Gibraltar on Thursday, the territory's Chief Minister Fabian Picardo said.

Two hundred corpses, including those of people believed to have been executed by the Islamic State group, were found near the Syrian city of Raqa, a local official and a war monitor said Wednesday.

Syria on Tuesday accused Israel of committing "state terrorism" after reported Israeli air strikes killed 15 people including civilians.

Four civilians, including a toddler, were killed and 21 injured in Israeli missile strikes near Damascus late Sunday, Syria's state news agency SANA reported.

An AFP correspondent in Damascus reported hearing loud explosions during the night.

The Syrian regime is co-opting aid and reconstruction assistance, Human Rights Watch said Friday, warning humanitarian players that they risked complicity in human rights abuses.

A Turkish soldier was killed and three others have been injured when the Syrian government fired on their observation post in the last rebel-held province of Idlib, Ankara said Friday. 

The "mortar and cannon shells" launched Thursday were a deliberate attack, the Turkish defence ministry said in a statement. 

Syria's state news agency says a bomb exploded in a car in Damascus, wounding a woman and her son. Activist groups said the victims were the wife and son of a pro-government political analyst.

SANA did not identify the two or say how seriously they were hurt in the explosion on Thursday morning. Opposition media activists and the Britain-based Syrian Observatory for Human Rights, a war-monitoring group, said the victims were analyst Taleb Ibrahim's wife and son. He was not in the car at the time of the blast.

Syrian government air strikes on the rebel-held northwest killed four civilians, two of them children, on Saturday, a war monitor said, as a two-month flare-up showed no let-up.

The Idlib region of some three million people is supposed to be protected by a September buffer zone deal, but the jihadist-run enclave has come under mounting bombardment by the government and its ally Russia since late April.

Fighting raged in northwest Syria on Thursday as clashes between regime forces and jihadist-led fighters killed more than 100 combatants in two days, a war monitor said.

The Idlib region, home to some three million people, is supposed to be protected by a months-old international truce deal, but it has come under increased bombardment by the regime and its Russian ally since late April.