UN-mandated human rights investigators said Monday they were probing 14 alleged chemical weapons attacks in Syria, but said they were still unable to pin the blame on either side.
"We're investigating 14 cases of alleged chemical weapons use," said Paulo Sergio Pinheiro, head of an independent commission inquiry set up by the UN Human Rights Council.
Pinheiro told reporters that given the difficulties in gathering evidence, it was still not possible to establish responsibility for the attacks, committed since the inquiry team started its work in September 2011, six months after the conflict began.
The comments came after he presented a fresh report on Syria to the Human Rights Council. A previous report had mentioned only four attacks, in March and April.
The commission steered by Pinheiro has been refused access to Syria by the regime of President Bashar al-Assad, which has also declined since October 2012 to respond to its requests for information.
But after holding out for almost a year, Syria appeared to have given some ground to the four-member team by last week when its UN ambassador invited former international war crimes prosecutor Carla del Ponte to visit the country.
Del Ponte, known for her relentless pursuit of criminals from the 1990s Balkan wars, said she rejected the invitation because she was only invited in a personal capacity and that the full team wanted access.
"I took the opportunity to speak with the Syrian ambassador and tell him that if, as it is said by the Syrian government, they were not using chemical weapons, it's time to invite the commission to investigate," she told reporters.
"I gave him an opportunity. I'm still expecting an answer," she added.
Pinheiro went to Syria in June 2012 after being invited in a personal capacity -- though he made it clear to Damascus that he was acting as head of the inquiry team, and rejected a subsequent invitation, he said Monday.
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Without access to Syria, the commission's investigation methods include meeting with Syrian refugees and carrying out telephone and Skype interviews with those inside the country.
Pinheiro said the team was also poring over videos of chemical attacks in Syria and receiving input from military experts.
Despite being unable to say who had deployed chemical weapons, Pinheiro earlier told the Human Rights Council that their use was clearly a war crime.
But he said that amid the global focus on Syria's chemical weapons, the use of deadly conventional arms should not be sidelined.
"The vast majority of the conflict's casualties result from unlawful attacks using conventional -- I repeat, conventional -- weapons such as guns and mortars," he told the council.
Under pressure over an August 21 chemical attack which the Syrian government's opponents say claimed over 1,400 lives, the Assad regime has signed an international treaty banning such arms.
Meanwhile, the United States and Syria's ally Russia struck a deal Saturday requiring Damascus to provide an inventory of its chemical weapons within days, and to allow inspectors in by November with a view to removing and destroying the arms by mid-2014.
The war in Syria, which erupted in March 2011, has claimed more than 100,000 lives and driven over two million refugees abroad, while millions of others have been displaced inside the country.
Pinheiro on Monday reiterated previous findings that regime loyalists were carrying out widespread attacks on civilians, committing murder, torture, rape and enforced disappearances.
He also slammed anti-government groups for war crimes including murder, torture and hostage-taking.
Both sides, he said, were also attacking hospitals and medical personnel, in another breach of the laws of war.