David Cameron has said any intervention in Syria would not be about the conflict itself but preventing the use of chemical weapons.
But the Prime Minister stressed that no decisions about British involvement have been made.
He said: "What we've seen in Syria are appalling scenes of death and suffering because of the use of chemical weapons by the Assad regime.
"I don't believe we can let that stand...any action we or others take will have to be legal, proportionate.
"Let me stress to people, this is not about getting involved in a Middle Eastern war or changing our stance in Syria, or going further into that conflict.
"It's about chemical weapons. Their use is wrong and the world should not stand idly by."