Barack Obama, the US president, has said the international community cannot remain silent in the face of the "barbarism" of the Syrian regime's alleged use of chemical weapons.
Obama told a news conference on Wednesday that "failing to respond to this attack would only increase the risk of more attacks and the possibility that other countries would use these weapons, as well."
The US president was speaking during a visit to Sweden ahead of the forthcoming G20 meeting in St Petersburg, Russia.
"I discussed our assessment [with the Swedish Prime Minister Fredrik Reinfeldt] and we are in an agreement that in the face of such barbarism the international community cannot be silent," he said.
He added that he hoped his Russian counterpart, Vladimir Putin, would change direction on a military intervention in Syria. Russia is Syria's biggest international ally.
"I'm always hopeful ... Ultimately, we can end deaths much more rapidly if Russia takes a different approach to these problems," he said.
Putin weighs in
His comments came hours after Putin warned the US against taking a one-sided action in Syria. He, however, also said in an interview that Russia "doesn't exclude" the possibility of supporting a UN resolution authorising military strikes.
He said that such an endorsement would require "convincing" evidence that President Bashar al-Assad's government used chemical weapons.
He also said the currently available evidence did not fulfil that criteria.
"From our viewpoint, it seems absolutely absurd that the armed forces, the regular armed forces, which... have encircled the so-called rebels and are finishing them off, that in these conditions they would start using forbidden chemical weapons," Putin said.
Figures vary regarding the alleged chemical weapons attack in a Damascus suburb on August 21, with the US government saying that 1,429 people were killed by poison gas in the attack, and aid agencies putting that number at closer to 355.
The Assad government has blamed the attack on the rebels, and a UN inspection team that examined the attack sites is awaiting lab results on soil and tissue samples.
"If there are data that the chemical weapons have been used, and used specifically by the regular army, this evidence should be submitted to the UN Security Council,'' Putin added in his interview.
"And it ought to be convincing. It shouldn't be based on some rumours and information obtained by special services through some kind of eavesdropping, some conversations and things like that."
He strongly cautioned the US against launching military action without the UN approval, saying it would represent an aggression.
Putin also said Russia had provided some components of the S-300 air defence missile system to Syria but that the delivery had not been completed.
He said that the process remained suspended "for now".
The interview on Tuesday night at Putin's country residence outside Moscow was the only one he granted prior to the summit of G-20 nations in St Petersburg, which opens on Thursday and will see major world powers discuss the global economy and the crisis in Syria.