President Vladimir Putin has refused to rule out supporting a military operation in Syria if there's clear evidence the Syrian government carried out a chemical weapons attack.
But Mr Putin says the United States hasn't yet produced that evidence and he's warning against United Nations backing for any such action.
His comments come as world leaders head to St Petersburg for the G20 summit.
The United States is continuing to try to marshal support for a military operation in Syria, just as Russia continues to ask for evidence proving the Syrian government was responsible for an alleged chemical weapons attack in Damascus on August the 21st.
Speaking in Stockholm en route to the G20 summit in St Petersburg, President Barack Obama says doing nothing about the attack is not an option.
"I do think that we have to act because if we don't we are effectively saying that even though we may condemn it and issue resolutions and so forth and so on, somebody who is not shamed by resolutions can continue to act with impunity."
In Washington, a Senate panel has approved the use of military force in Syria and the matter will now go to a full Senate vote, which is expected next week.
Russia's President Vladimir Putin says the US would need to present clear evidence of Syrian government involvement before he'd consider supporting an action which he says would have to have UN backing.
"We think that if someone has evidence proving that chemical weapons have been used, and that it was the regular army that used them, they should present this evidence to the UN Security Council, to the inspectors and to the Security Council. This evidence has to be compelling: it should not just be hearsay, just some conversations intercepted by the intelligence service. Even in the US some experts think the evidence presented by the administration is not compelling, it is possible that the opposition staged a provocation in order to give their patrons an excuse for a military intervention."
Mr Putin says the horrific video footage of dead children posted on the internet following the alleged attack is suspicious because of what it doesn't show.
"I'd like to point out that there are no parents, women or medical personnel in those pictures which you would have noticed at a closer look. Who are those people and what really happened there? This question remains open, certainly those pictures are just hideous but they don't prove anyone guilty. This incident obviously has to be investigated. We would like to know who is responsible for these atrocities."
Mr Putin says the Syrian crisis is likely to be discussed at the G20 summit.
"The G20 summit will mainly focus on the world economy and economic problems such as slow economic growth, unemployment, corruption, tax crimes and management but considering the grave situation in Syria and that we can't agree on what is to be done to resolve this extremely important issue, we could probably take advantage of the fact that the leaders of the 20 leading economies of the world will be meeting in Saint Petersburg and spend some time discussing this topic. We will not impose it though, we can just propose to deviate from the agreed agenda and discuss the Syrian conflict."
Aside from Syria, reforming tax laws is one key agenda item at the G20.
There are calls for countries to rewrite their tax laws because the existing laws currently allow companies to underpay taxes owed to African countries.
The charity, Oxfam, says it's the result of a practice known as profit-shifting, where companies work in a developing country but register their earnings - and pay taxes - in a different country.
Oxfam says African countries are losing almost two per cent of their gross domestic product each year because of the practice.
The OECD is also seeking stronger action against tax cheats, by countries agreeing to an automatic exchange of banking data.
