The Assad regime has begun to evacuate military command headquarters in the Syrian capital of Damascus ahead of a possible US-led military strike.
Personnel from army and security command headquarters including the General Staff Command Building, Umayyad Square, the nearby air force command and other security compounds in the Western Kfar and Souseh districts have been partially evacuated, according to Reuters.
Obama's reported plans for a one-off strike have been described as limited in scope and duration, aimed at punishing the Syrian regime but with the lowest possible death toll. The attack, which would last no more than two days, would involve sea-launched cruise missiles on an almost-empty military infrastructure, according to reports.
Russia has again voiced its opposition to a UN resolution authorising military action to protect civilians in Syria, saying it was "premature".
British foreign secretary William Hague said he would prefer a united UN over Syria's intervention, however unlikely that seemed.
"We are looking for a clear and proportionate response. It's important to respond to what has happened. It's important not to take so long and for Assad regime to know that there's a clear response," he said.
He called the use of chemical weapons in Ghouta a crime against humanity and "the first use of chemical warfare in the 21st century".
Asked why Britain would not wait until UN inspectors in Damascus finish their investigation, Hague said: "We have to be realistic to what UN inspectors can achieve. UN teams have no mandate to blame one side or the other for the attack. But all evidence points on one direction."
He also rejected any comparison with the 2003 Iraqi war.
"It's an entirely different situation," said Hague. "The Syrian regime acknowledges it has chemical weapons. One hundred thousand have died in Syria, there are two million refugees and chemical weapons were used. We are also seeking authorisation from the Security Council."
Labour leader Ed Miliband said he told the prime minister that any military action in Syria "must have a proper, sound legal base in international law".