Damascus:
A US pledge to step up military aid to Syrian rebels because of alleged use of chemical arms by the regime drew criticism from Damascus ally Russia and from UN chief Ban Ki-moon on Friday.
Syria itself dismissed the accusation as "lies."
The UN secretary general said arming either side in the 27-month war, which has cost tens of thousands of lives, "would not be helpful".
Ban said he has been "consistently clear that providing arms to either side would not address this current situation. There is no such military solution."
The harder US line also dismayed Moscow, which had been working with Washington to organise a peace conference.
US data on chemical weapons was "unconvincing", it said, warning Washington against repeating the mistake it made when invading Iraq after falsely accusing Saddam Hussein of stocking weapons of mass destruction.
Top Kremlin foreign policy adviser Yury Ushakov also said the US decision to provide military aid to Syrian rebels would damage international efforts to end the conflict.
Russian President Vladimir Putin and US President Barack Obama are to meet at the G8 summit in Northern Ireland on Monday.
The US decision prompted Sweden to warn of the danger of an arms war between rival foreign backers of the regime and the rebels.
The conflict in Syria topped the agenda in a video conference on Friday among G8 leaders ahead of next week's summit, British and French officials said.
Obama's administration announced late on Thursday that it had reviewed intelligence reports and concluded that regime forces had used banned weapons, including sarin, in attacks that killed up to 150 people.
US officials refused to rule out moving towards arming rebels, and said Washington would provide backing to the rebel Syrian Military Council.
Britain and France, which had already said they believed the Syrian government had resorted to using its chemical weapons stockpiles, welcomed the US announcement.
But Damascus dismissed it as "a statement full of lies" and asked how Washington could continue to be regarded as an honest broker in any UN-backed peace conference.