As the civil war in Syria marks its fifth anniversary this month, a new report released by U.S.-based nonprofit, the Syrian American Medical Society (SAMS), claims that 161 chemical attacks have taken place in the Middle Eastern country since fighting began. The report also says that 2015 was the worst year, in terms of use of chemical weapons, and that chemical attacks are still ongoing.

The documented 161 attacks have killed 1,491 people and injured another 14,581, according to the report, which added that 77 percent of the attacks took place after United Nations Security Council passed a resolution in 2013 creating a framework for the destruction of Syria’s chemical weapons stockpiles. It also said that at least 58 attacks that use chlorine took place after the adoption of another UNSC resolution that declared chlorine gas a weapon in Syria.

SAMS compiled its data using first-hand accounts and other reports from physicians and healthcare workers in Syria. The nonprofit found another 133 cases of reported chemical attacks but could not verify them.

While 2015 was the year with the maximum number of chemical attacks, the deadliest attacks took place in Aug. 21, 2013, when rockets filled with sarin were launched into rural Damascus, killing over 1,300 people and injuring more than 10,000.

The SAMS report said that non-state actors such as the Islamic State group have also started using chemical weapons and that their use is continuing, spurred by the “lack of enforcement of international humanitarian and human rights law and several UNSC resolutions.”

Meanwhile, peace talks between the government and various opposition groups, with the aim to end the ongoing conflict in Syria, began in Geneva Monday.