United Nations (United States) (AFP) - A UN investigative team has zeroed in on five potential cases of serious chemical weapons use in Syria but has yet to identify the perpetrators, according to its first report released Friday.

The Joint Investigative Mechanism was established by the UN Security Council in August last year to come up with a list of names of those responsible for attacks using toxic chemicals in Syria.

In its first report, the panel told the Security Council it wanted to further investigate five chemical weapons attacks in Syria's Hama, Idlib and Aleppo provinces, that took place in 2014 and 2015.

"The process of identifying those involved in the use of chemicals as weapons is a complex task for which the mechanism will require the continued support and cooperation of all states and other sources," the panel said in the report.

The investigative panel was set up after evidence surfaced of chlorine gas attacks on three Syrian villages in 2014 that left 13 dead.

President Bashar al-Assad's regime and rebel groups have accused each other of using chemical weapons in the nearly five-year war that has killed more than 250,000 people.

The report did not provide details, but four of the five cases point to the alleged use of chlorine gas in barrel bombs, that the West blames on the Syrian regime.

These took place in Kafr Zita on April 11 and 18, 2014, Talmenes on April 21, 2014, Qmenas on March 16, 2015, and Sarmin on March 16, 2015.

A more recent attack in Marea on August 21, 2015, pointed to the likely use of mustard gas by Islamic State militants.

The panel said it may add more cases for investigation to its current list of five attacks.

The Organization for the Prohibition of Chemical Weapons has identified 116 alleged incidents of use of chemicals as weapons, but the body has no mandate to assign blame for the attacks.

The panel headed by Argentine expert Virginia Gamba traveled to Damascus in December to press the government for cooperation and intends to push for access to locations and witnesses for its investigation, the report said.