Any chemical weapons attack in Syria would constitute a "crime against humanity," UN chief Ban Ki-moon said on Friday, adding there was "no time to lose" in investigating their alleged use near Damascus.
In impromptu remarks at a scheduled event in Seoul, the secretary general said the reports of a chemical attack on civilians near the Syrian capital were "very alarming and shocking".
"Any use of chemical weapons anywhere, by anybody, under any circumstances, would violate international law," Ban said.
"Such a crime against humanity should result in serious consequences for the perpetrator," he added.
A UN inspection team is already on the ground in Syria and Ban urged the Syrian authorities to cooperate with their immediate probe into the alleged attack near Damascus which the opposition says killed hundreds.
"This is a grave challenge to the entire international community - and to our common humanity, especially considering it occurred when the United Nations expert mission is in the country," Ban said.
"I can think of no good reason why any party - either government or opposition forces - would decline this opportunity to get to the truth of the matter. "
Footage distributed by activists showing unconscious children, people foaming around the mouth and doctors apparently giving them oxygen to help them breathe has triggered revulsion around the world.
"There is no time to waste," Ban said, adding that he had instructed his envoy for disarmament affairs, Angela Kane, to travel to Damascus immediately.
"The Syrian people have suffered enough far too long," he said, calling on all sides to the conflict to lay down their arms immediately and initiate a dialogue.