UN warcrimes investigators know of 14 potential chemical attacks in Syria since the began monitoring Syrian human rights abuses in September 2011, the team's chairman said on Monday.
"We are investigating 14 alleged cases of chemical weapons or chemical agent use. But we have not established the responsibility or the nature of the materials that were used," Paulo Pinheiro, chairman of the UN Commission of Inquiry on Syria told a news conference.
"We don't have to share where, or when, or what moment. We don't have to elaborate more on that."
Pinheiro also said Syria had invited commission member Carla del Ponte to visit Syria in a personal capacity, but the commission wanted an official visit, including him.
Del Ponte said it was assumed she had been invited to Syria because she said publicly in May that the commission had allegations that opposition groups had used chemical weapons, but said that she did not know for sure.
However, the commission, which was set up two years ago by the UN human rights council, has been invited to Saudi Arabia and Iran - backers of the opposition and Syrian government, respectively - and intends to go next month, Pinheiro said.
The commission's lead members were speaking after presenting their latest report to the UN Human Rights Council in Geneva, and shortly before UN chemical weapons inspectors present their report to the UN secretary general in New York.
While the weapons inspectors may confirm the use of a chemical weapon, it is up to the Commission of Inquiry to try to find out who was responsible and bring them to justice.
Without having access to the country, they gather information from witness testimony and try to verify and crosscheck reports from inside Syria.
"I think that the report from the special experts on the use of chemical weapons will be a big step for us, forward in our investigation," Del Ponte said.
"But for sure we must enter Syria, to have a proper, judicial, formal investigation on that and to know exactly who was using chemical weapons."