UN Secretary General Ban Ki-moon warned on Friday that the use of chemical weapons in Syria would carry serious consequences.
Syrian President Bashar Assad's opponents gave death tolls from 500 to well over 1,000 and said more bodies were being found in the wake of Wednesday's mysterious pre-dawn killer fumes, which the Syrian government insists were not its doing.
Ban said he was troubled by the reports that chemical weapons might have been used in Syria.
"Any use of chemical weapons anywhere by anybody under any circumstances would violate international law. Such a crime against humanity should result in serious consequences for the perpetrator," said Ban.
"I have called on the Syrian government to extend its full cooperation so that the mission can swiftly investigate this most recent incident," he added during a speech at a breakfast meeting with diplomats in South Korea.