UN Secretary-General Ban Ki-moon has urged the Security Council to impose an arms embargo on Syria, describing foreign powers and groups as "irresponsible" for giving military support to the warring parties in the three-year conflict.
"If divisions in the Council continue to prevent such a step, I urge countries to do so individually," said Ban on Friday.
Russia, supported by China, has shielded Syria on the Security Council during the conflict by vetoing four resolutions that threatened action against Bashar al-Assad's government. Russia is also one of Syria's main arms suppliers.
The United States is supplying rebels with "non-lethal" aid - such as radios, trucks and training. But some US officials say small arms and anti-tank missiles are also being given.
"Syria's neighbours should enforce a firm prohibition on the use of their land borders and airspace for arms flows and smuggling into Syria," he said.
'A failed state'
Ban expressed anger and disappointment that the international community has been unable to find a way to end the civil war that has killed about 150,000 people, displaced half the country's 22 million population and forcing 2.8 million to flee.
"Syria today is increasingly a failed state," he said. "The Syrian conflict has now spread visibly and devastatingly to Iraq, with flows of arms and fighters across a porous border."
International and regional powers have backed opposing sides, with Russia and Iran supporting Syrian Assad and Western powers and Gulf Arab states largely backing the rebels. The UN Security Council has been largely deadlocked.
Ban welcomed recent contacts between Iran and Saudi Arabia and expressed hope that "they will build confidence and reverse a destructive competition in Syria, Iraq, Lebanon and elsewhere".