Arming Syrians on either side of the country's bloody conflict could lead to more war crimes, the head of the UN commission investigating human rights abuses has warned.
Paulo Pinheiro stopped short of directly criticising the United States or other nations arming Syrians, saying the commission does not comment on decisions by governments, but his remarks came about a week after president Barack Obama authorised sending weapons to rebels.
It marked a major policy shift for the Obama administration, and came after the White House disclosed that the US had conclusive evidence that Bashar Assad's regime had used chemical weapons against the opposition trying to overthrow him.
"States who provide arms have a responsibility in terms of the eventual use of these arms to commit gross human rights violations, war crimes or crimes against humanity," Mr Pinheiro said. "We are very much worried that more arms will signify an increased presence of violations and those crimes."
The UN Commission of Inquiry earlier this month in a report to the UN Human Rights Council in Geneva accused both sides of committing war crimes in Syria. About 93,000 people have been killed since the protests began in March 2011.
"Crimes that shock the conscience have become reality. We emphasise that there is a devastating human cost to the availability of weapons and that there is also a political cost," Mr Pinheiro said. "Weapons fuel the parties' illusion that they can win this war, pulling them farther into battle and away from the negotiating table."
He reiterated his support for a Syria peace conference called for by Russia and the United State that would bring together rebels of the Free Syrian Army and forces of Assad. No date for those talks has been set, but leaders at the G8 who met this week in Northern Ireland all agreed talks should start soon.
In its report, the commission also found there were "reasonable grounds" to believe that limited quantities of toxic chemicals had been used as weapons in at least four attacks in Syria's civil war, but that more evidence was needed to determine the precise chemicals agents used or who used them.
The commission said conclusive findings could only be reached by getting testing samples directly from victims of the attack, and UN chemical weapons experts still have not been allowed to enter Syria.
In Syria, rebels said they had received shipments of new weapons from Arab nations and other countries, though none yet from the US.