Syria's deputy foreign minister Faisal Mekdad denounced any armed Western move against his government. "A decision to wage war on Syria is a criminal decision and an incorrect decision. We are confident that we will be victorious," he told reporters outside a hotel in Damascus.
However, Syria's opposition coalition called on Sunday on the U.S. congress to grant approval for military action and said any intervention should be accompanied with more arms for the rebels.
Obama made his surprise announcement in a gamble that will test his ability to project American strength abroad and deploy his own power at home.
Before he put on the brakes, the path had been cleared for a U.S. assault. Navy ships were in place and awaiting orders to launch missiles, and U.N. inspectors had left Syria after gathering evidence of a chemical weapons attack that U.S. officials say killed 1,429 people in rebel-held areas.
The United States had been expected to lead the strike soon, backed up by its NATO allies Britain and France. However, the Westminster parliament voted last Thursday against any British involvement and France said on Sunday it would await the U.S. Congress's decision.
"France cannot go it alone," Interior Minister Manuel Valls told Europe 1 radio. "We need a coalition."
(Read more: Obama to seek OK from Congress for action in Syria)
France, which ruled Syria for more than two decades until the 1940s, has, like the United States and Britain, the military strength to blitz the country in response to the poison gas attack on areas around Damascus, which the Syrian government has accused the rebels of staging.
Valls said Obama's announcement had created "a new situation" which meant France would have to wait "for the end of this new phase".
President Francois Hollande reaffirmed to Obama on Saturday his will to punish Syria but has come under increasing pressure to put the intervention to parliament.
A BVA poll on Saturday showed most French people do not approve of military action against Syria and most do not trust Hollande to conduct such an operation.
His prime minister Jean-Marc Ayrault is scheduled to meet the heads of the two houses of the French parliament and the conservative opposition on Monday before a parliamentary debate on Syria on Wednesday.
Last month's attack was the deadliest incident of the Syrian civil war and the world's worst use of chemical arms since Iraq's Saddam Hussein gassed thousands of Kurds in 1988.
However, polls also show strong opposition to a strike on Assad's forces among Americans weary of wars in Iraq and Afghanistan. Congressional approval will more than a week, if it comes at all.
A senior Syrian rebel expressed concern about the delay, saying it gave Assad and his government the chance to keep killing and prepare from a missile or bomb attack.
"As days go by, more people get killed by the hands of this regime. Further delay for action gives them a chance to change the position of their weapons," said Mohammad Aboud, the Deputy Commander of eastern joint command of the Free Syrian Army.
"According to the intelligence that we have, we know that he exploits this delay to prepare for this strike," Aboud, a lieutenant who defected from Assad's forces, told Reuters.
Foreign Ministers from the Arab League, which blamed Syria for the chemical attack but has so far stopped short of explicitly endorsing Western military strikes, are due to meet in Cairo on Sunday.
Some analysts believe Syria could strike back at its neighbors in retaliation for any Western attack. On Sunday Israeli Prime Minister Benjamin Netanyahu did not mention Syria by name, but said: "Israel is serene and self-confident."
"Israel's citizens know well that we are prepared for any possible scenario. And Israel's citizens should also know that our enemies have very good reasons not to test our power and not to test our might," he said in public remarks to his cabinet before its weekly meeting.
Obama's credibility had already been called into question for not punishing Assad over earlier alleged gas attacks, and he is under pressure to act now that he believes Damascus has crossed what he once described as a "red line."
Some analysts say that if Assad goes unpunished, Iran will feel entirely free to press on with its nuclear program. Tehran says this is peaceful but the West believes it wants to develop nuclear weapons. Any U.S. failure to act might encourage Israel to take matters into its own hands, say analysts.
(Read more: The hardware the US military will use to strike)
"If Obama is hesitating on the matter of Syria, then clearly on the question of attacking Iran—a move that is expected to be far more complicated—Obama will hesitate much more, and thus the chances Israel will have to act alone have increased," Israeli Army Radio quoted an unnamed government official as saying.
Iranian Parliament Speaker Ali Larijani said world opinion stood against any attack on its ally Syria, pointing to the British parliament's rejection of military action.
In the Vatican City, Pope Francis called for a negotiated solution to the conflict in Syria and announced he would lead a worldwide day of prayer for peace in the country on Sept. 7.