Syria in the mid of the US-Western storm of military intervention.
However, with the escalation in the tone of Damascus allies, US President Barack Obama found no way out to delay the action, in a search for a UN cover.
Obama announced Wednesday he had not yet signed off on a plan to strike Syria, but action appeared likely after Washington abandoned the hunt for a last-minute UN mandate.
This comes as political uproar in London, meanwhile, cast doubt on whether Britain will join American military action, should the response take place before next week.
A senior White House official told Agence France Presse that the administration will brief senior US lawmakers on Thursday about classified intelligence about the alleged chemical attack.
Asked how close he was to ordering a US strike, expected to start with cruise missile raids, Obama told PBS NewsHour: “I have not made a decision.”
But he warned that US action would be designed to send a “shot across the bow” to convince Syria it had “better not do it again.”
Meanwhile, the US President claimed that the limited strikes envisioned by the White House would not stop the killing of civilians in Syria but said he had decided that getting involved in a civil war that has already killed 100,000 people would not help the situation.
“We do have to make sure that when countries break international norms on weapons like chemical weapons that could threaten us, that they are held accountable,” Obama said.
Earlier, Washington bluntly signaled that a UN Security Council resolution proposed by Britain that could have given a legal basis for an assault was going nowhere, owing to Russian opposition.
“We see no avenue forward, given continued Russian opposition to any meaningful Council action on Syria,” State Department deputy spokeswoman Marie Harf said.
“We cannot be held up in responding by Russia’s continued intransigence at the United Nations, and quite frankly the situation is so serious that it demands a response,” Harf said.
British Prime Minister David Cameron was meanwhile slowed by a parliamentary revolt and was forced to pledge he would not order military action until the report by UN inspectors has been published.
Cameron plans to put his case to lawmakers on Thursday, but with a majority in doubt on the issue a second vote, possibly early next week, will now have to take place before British forces can join the fray.
White House officials would not immediately say whether Washington would wait for Britain before launching any military action.