Damascus: Syria and Russia have both slammed US allegations that Syrian government forces have used chemical weapons against opposition fighters in the country's civil war, with the Syrian government terming the charge "full of lies".
The commander of the main rebel umbrella group has welcomed the US move, saying that it would lift his fighters' morale.
President Barack Obama's deputy national security adviser, Ben Rhodes, said the US president was planning to step up military assistance to Syrian rebels, as a response to intelligence estimates indicating the use of chemical weapons in the conflict.
"The White House has issued a statement full of lies about the use of chemical weapons in Syria, based on fabricated information," a statement issued on Friday by the Syrian Foreign Ministry said.
"The United States is using cheap tactics to justify President Barack Obama's decision to arm the Syrian opposition," it said.
The statement also accused the US of "double standards", by combatting terrorism while providing support for "terrorist" groups in Syria, such as Jabhat al-Nusra, with arms and money. The group, also known as the Nusra Front, is an al-Qaeda affiliate that has emerged as one of the most effective rebel factions in Syria.
Russia, a staunch ally of the Syrian government, also disputed the US charge on Friday.
President Vladimir Putin's foreign affairs adviser, Yuri Ushakov, told reporters that the information provided by US officials to Russia "didn't look convincing".
Asked if Russia could retaliate to the US move to supply weapons to the Syrian rebels by delivering the S-300 air defence missile systems to the regime, Ushakov said "there is no talk about it yet".
"We aren't competing over Syria, we are trying to settle the issue in a constructive way," he said.
On Friday, UN Secretary-General Ban Ki-moon said that "the validity of any information on the allege use of chemical weapons cannot be ensured without convincing evidence of the chain-of-custody", and said increasing the flow of arms to either side "would not be helpful".