Summary The conflict in Syria has reached new levels of brutality. This report documents for the first time the systematic imposition of sieges, the use of chemical agents and forcible displacement. War crimes, crimes against humanity and gross human rights violations continue apace. Referral to justice remains paramount. This report covers the period 15 January to 15 May 2013. The findings are based on 430 interviews and other collected evidence. Government forces and affiliated militia have committed murder, torture, rape, forcible displacement, enforced disappearance and otherinhumane acts. Many of these crimes were perpetrated as part of widespread or systematic attacks against civilian populations and constitute crimes against humanity. War crimes and gross violations of international human rights law – including summary execution, arbitrary arrest and detention, unlawful attack, attacking protected objects, and pillaging and destruction of property – have also been committed. The tragedy of Syria's 4.25 million internally displaced persons is compounded by recent incidents of IDPs being targeted and forcibly displaced. Anti-Government armed groups have also committed war crimes, including murder, sentencing and execution without due process, torture, hostage-taking and pillage. They continue to endanger the civilian population by positioning military objectives in civilian areas. The violations and abuses committed by anti-Government armed groups did not, however, reach the intensity and scale of those committed by Government forces and affiliated militia. There are reasonable grounds to believe that chemical agents have been used as weapons. The precise agents, delivery systems or perpetrators could not be identified. The parties to the conflict are using dangerous rhetoric that enflames sectarian tensions and risks inciting ma**, indiscriminate violence, particularly against vulnerable communities. War crimes and crimes against humanity have become a daily reality in Syria where the harrowing accounts of victims have seared themselves on our conscience. There is a human cost to the increased availability of weapons. Transfers of arms heighten the risk of violations, leading to more civilian d**hs and injuries. A diplomatic surge is the only path to a political settlement. Negotiations must be inclusive, and must represent all facets of Syria's cultural mosaic. IV D. Illegal Weapons 136. As the conflict escalates, the potential for use of chemical weapons is of deepening concern. Chemical weapons include toxic chemicals, munitions, devices and related equipment as defined in the 1997 Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and Their Destruction. Also applicable is the 1925 Geneva Protocol which Syria has ratified. The use of chemical weapons is prohibited in all circumstances under customary international humanitarian law and is a war crime under the Rome Statute. 137. The Government has in its possession a number of chemical weapons. The dangers extend beyond the use of the weapons by the Government itself to the control of such weapons in the event of either fractured command or of any of the affiliated forces gaining access. 138. It is possible that anti-Government armed groups may access and use chemical weapons. This includes nerve agents, though there is no compelling evidence that these groups possess such weapons or their requisite delivery systems. 139. Allegations have been received concerning the use of chemical weapons by both parties. The majority concern their use by Government forces. In four attacks – on Khan Al-Asal, Aleppo, 19 March; Uteibah, Damascus, 19 March; Sheikh Maqsood neighbourhood, Aleppo, 13 April; and Saraqib, Idlib, 29 April – there are reasonable grounds to believe that limited quantities of toxic chemicals were used. It has not been possible, on the evidence available, to determine the precise chemical agents used, their delivery systems or the perpetrator. Other incidents also remain under investigation. 140. Conclusive findings – particularly in the absence of a large-scale attack – may be reached only after testing samples taken directly from victims or the site of the alleged attack. It is, therefore, of utmost importance that the Panel of Experts, led by Professor Sellström and a**embled under the Secretary General's Mechanism for Investigation of Alleged Use of Chemical and Biological Weapons, is granted full access to Syria.