The United States may take unilateral action in Syria if the United Nations fails to respond to a suspected chemical attack in Syria which is feared to have killed dozens of civilians, including children, the country's UN ambassador has warned.

The warning came as the UN Security council held an emergency meeting about the atrocity, after Washington, Paris and London drew up a draft statement condemning the attack and demanding an investigation.

"When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action," Nikki Haley, the U.S. Ambassador to the United Nations, told the meeting.

Earlier Russia has threatened to veto any resolution by the UN security council on a claiming it is based on "false information."

"Unfortunately, based on totally fake information, the United States, France and Great Britain have once again planted - one cannot put it any other way - into the U.N. Security Council a draft resolution which has a completely anti-Syrian character," said Russian foreign ministry spokeswoman Maria Zakharova.

US defence secretary Jim Mattis hit back, saying the attack was "a heinous act and will be treated as such."