Russia has warned that a peace conference to end the conflict in Syria could be put off "forever" if the US goes ahead with military action against the regime.
Foreign minister Sergei Lavrov warned that the planned discussions in Geneva would be disrupted by a US strike.
"If the action announced by the US President - to the great regret of all of us - does in fact take place ... it will put off the chances of (holding) this conference for a long time, if not forever."
As tension mounts between Moscow and Washington over the situation, Russia has sent a spy ship to the eastern Mediterranean.
According to Russian news agency Interfax, the ship left a naval base in the Ukrainian Black Sea port of Sevastopol late on Sunday on a mission "to gather current information in the area of the escalating conflict".
Russia's parliament has also said it will seek to speak to the US Congress to ask for a "balanced" response to the Syria issue.
Any military action hinges on whether President Bashar al Assad’s regime was responsible for a chemical weapons attack in Syria last month in which 1,429 people - including at least 426 children - died.
France says it has new evidence that the Government was responsible, and will hand it over to lawmakers later.
Washington has already announced that hair and blood samples prove the regime has used sarin gas to attack civilians.
Secretary of State John Kerry has used interviews with several US news channels to suggest the case for military strikes is growing, adding that he is confident Congress will back military action when it is put to a vote next week.
The nuclear-powered USS Nimitz aircraft carrier is moving westward toward the Red Sea, although it has not yet received orders to support a potential strike.
In Britain there have been calls for David Cameron to consider a second parliamentary vote on military action in Syria.
Mayor of London Boris Johnson has become the latest senior politician to suggest a new bid for parliamentary support could be made.
Mr Johnson said the use of chemical weapons for mass murder in Syria could not go unpunished.
"If there is new and better evidence that inculpates Assad, I see no reason why the Government should not lay a new motion before Parliament, inviting British participation - and then it is Ed Miliband, not David Cameron, who will face embarrassment," Mr Johnson wrote in The Telegraph.
Mr Cameron ruled out the use of British force in Syria following a defeat in the Commons.
Deputy Prime Minister Nick Clegg has also said he could not foresee any circumstances in which the Government would return to Parliament on the same issue.
"We're not going to keep asking the same question of Parliament again and again. We live in a democracy, the executive cannot act in a way which clearly is not welcome to Parliament or the British people, so we're not proposing to do so."
Arab League ministers have urged the United Nations and the international community to take "deterrent" action, while blaming the regime for the alleged chemical weapons assault.
However a defiant Mr Assad told state TV his country is capable of confronting any attack.
"The American threats of launching an attack against Syria will not discourage Syria away from its principles ... or its fight against terrorism supported by some regional and Western countries, first and foremost the United States of America," he said.
As the diplomatic wrangling continues, British MPs have called for answers from the Government over a chemicals trade deal with Syria signed months after the bloodshed started.
The Department for Business issued licences for the export of sodium fluoride and potassium fluoride to the war-torn country in January last year before revoking them several months later.
The chemicals are capable of being used to make nerve gas such as sarin as well as having a variety of industrial uses.
The Government said no chemicals were exported before the licence was revoked in June 2012 following EU sanctions but MPs said they intend to raise the issue at Westminster.
The UN has announced that seven million people have been displaced by the ongoing civil war.
Fears in Israel that the fallout from any attack on Syria could spill across their northern border and drag the Jewish state into the conflict, Israelis last week rushed to replace their old gas masks.
