The Syrian Observatory for Human Rights said a series of strikes launched from Russian warships and by allied Syrian government forces hit the makeshift refineries in Aleppo province on Friday night, causing a massive blaze as dozens of tankers caught fire in the area controlled by Turkey and its Syrian rebel proxies.

The Britain-based monitor "documented the deaths of four people, while 24 others sustained various injuries and burns" in the attacks near the towns of Jarablus and Al-Bab.

At least one Syrian rebel was among the dead, said Observatory head Rami Abdul Rahman.

Rescue workers spent hours trying to extinguish the fire which spread to about 180 oil tankers, according to the war monitor.

"The fires are the largest yet from a missile attack on makeshift refineries," the Observatory said.

Oil installations in Turkey-controlled parts of Aleppo have come under repeated attack in recent months although Moscow and the Syrian regime have not claimed responsibility.

The Observatory reported two such missile attacks last month.

In January, unidentified drones also hit oil refineries in Turkish-held areas of Aleppo, causing a large fire, according to the Observatory.

Syria's war has killed more than 387,000 people and displaced millions since starting in 2011 with a brutal repression of anti-government protests.

It later evolved into a complex conflict involving jihadists and foreign powers.

Northern neighbour Turkey has seized control of several regions inside Syria in military campaigns against the Islamic State group and Kurdish fighters since 2016.