French foreign minister Laurent Fabius has urged the international community to react with force if allegations that the Syrian government used chemical weapons to kill hundreds of civilians are proved true.

He stopped short of calling for military intervention on the ground, adding that if the UN security council could not make a decision, one would have to be taken "in other ways".

"There would have to be reaction with force in Syria from the international community, but there is no question of sending troops on the ground," he told news channel BFMTV.

Britain and France have been the most hawkish of the EU countries regarding a possible military intervention in Syria, but the UK's foreign secretary William Hague did not echo Fabius' words.

"I hope this will wake up some who have supported the Assad regime, to realise its murderous and barbaric nature," he said in Paris.

Israel has claimed that chemical weapons were used in the attack. Yuval Steinitz, the minister for intelligence and strategic affairs, blamed Assad's "exceptionally cruel" regime for the deployment of chemical weapons that killed at least 100 people, but did not elaborate.

The UN security council convened an emergency meeting to look into allegations by the Syrian rebels that more than 1,000 people were killed by a barrage of rockets with toxic agents, launched by government forces into the eastern Damascus suburbs of Ghouta.

The Syrian government has denied the reports, saying they were "illogical and fabricated".

UN officials called the attack a "serious escalation" and urged clarity over the use of chemical weapons.

Security Council members "welcomed the determination of the Secretary-General (Ban Ki-moon) to ensure a thorough, impartial and prompt investigation", she added.

However, the council stopped short of calling collectively for a UN investigation, with China and Russia providing strong opposition.