Investigators at the United Nations today announced that chemical weapons were likely used in Syria earlier this year, though it remains unclear whether they were deployed by President Bashar al-Assad or the opposition groups looking to depose him. The UN detailed its findings in a 29-page report examining four chemical attacks allegedly staged in March and April.

Human rights investigators conducted more than 400 interviews with refugees, nurses, and victims in affected areas, with most witnesses alleging that the weapons were used by Assad's army. Assad and rebel leaders have accused each other of using chemical agents, which US President Barack Obama has publicly described as a "red line" that could trigger American intervention. In April, the White House said it was likely that Assad had used sarin gas against the rebels, corroborating similar findings from British and French intelligence.

"The conflict in Syria has reached new levels of brutality."

"There are reasonable grounds to believe that limited quantities of toxic chemicals were used," Paulo Pinheiro, chairman of the UN's commission of inquiry, said Tuesday at a press conference in Geneva. "It has not been possible, on the evidence available, to determine the precise chemical agents used, their delivery systems or the perpetrator."

Pinheiro added that the attacks were conducted on a relatively small scale, noting that they resulted in far fewer casualties than conventional operations. In its report, the UN acknowledged that both Assad and rebel groups are guilty of committing crimes against humanity, including widespread murder, rape, and torture.

"The conflict in Syria has reached new levels of brutality", the UN said in its report. "War crimes, crimes against humanity and gross human rights violations continue apace."

But crimes committed by the government, the agency says, were carried out on a much larger and more violent scale. Thus far, an estimated 80,000 people have been killed in Syria since civil unrest broke out more than two years ago.

"The documented violations are consistent and widespread, evidence of a concerted policy implemented by the leaders of Syria's military and government," reads the report, the fifth that the UN has published since the beginning of the Syrian civil war.

"Accountability will come"

The UN Human Rights commission urged the Security Council to take action against those responsible. "Accountability will come, it will come in any case," commission member Carla del Ponte, a former UN war crimes prosecutor, told reporters Tuesday.

A separate team of UN chemical warfare experts has been trying to conduct tests on soil and victims in Syria, but they have been repeatedly denied access. According to the UN, these tests are critical to determining the agents used, and the party that deployed them.