British Prime Minister David Cameron has held an emergency meeting to discuss the UK's response to the deepening crisis in Syria.
A National Security Council (NSC) meeting took place at the PM's offices in Downing Street today.
The prime minister said the world could "not stand idly by" in the face of the "massive use" of banned weapons.
But any military action would have to be legal, he added. Meanwhile, America has said its forces are "ready to go".
At today's meeting, the National Security Council "agreed the use of chemical weapons by Assad was unacceptable and the world cannot stand by", Mr Cameron said.
The Syrian government says it was not responsible for last week's chemical attack - and that America and others were using it as an excuse to attack.
Later today, powerful countries will meet at the United Nations in New York to discuss what the UN could do to protect people in Syria.
But not everyone agrees that Britain should be so quick to get involved.
The opposition Labour party has said that it won't support the government's plans until the UN weapons inspectors make a report about the chemical attack.
The Archbishop of Canterbury Justin Welby earlier warned MPs not to rush any decision saying the consequences of military action across the Muslim world were unpredictable.
Why has the situation changed?
Last week's poison gas attack - in which more than 300 people are thought to have died - has led to a change in the way world leaders have spoken about the Syrian conflict.
US President Barack Obama called it a "big event of grave concern", and he and Mr Cameron said that there would be a "serious response" from Britain and the US.
BBC correspondent Frank Gardner says it is the horror of Wednesday's attack that's driven the British, French and American governments to say that something must be done now, otherwise whoever carried out the attack will do it again.