On Sunday, U.S. Secretary of State John Kerry said Washington received new physical evidence in the form of blood and hair samples that show sarin gas was used in the attack. It wasn't immediately clear whether that evidence had been shared with Russia.
U.N. chemical inspectors toured the stricken areas last week, collecting biological and soil samples. A U.N. statement said the team "worked around the clock" to finalize preparations of the samples, which were shipped Monday afternoon from The Hague and would reach their designated laboratories "within hours," the statement said.
Secretary-General Ban Ki-moon planned to brief the Security Council's 10 non-permanent members on the Syria crisis Tuesday morning. Angela Kane, high representative for disarmament affairs, planned a Tuesday briefing for member states that requested the investigation of alleged chemical weapons use in the Ghouta area outside Damascus on Aug. 21.
The Obama administration has failed to bring together a broad international coalition in support of military action, having so far only secured the support of France.
Britain's Parliament narrowly voted against the country's participation in any military strike last week, despite appeals by Prime Minister David Cameron. The Arab League has stopped short of endorsing a Western strike against Syria.
In an emergency meeting Sunday, the 22-state League urged the United Nations and the international community to take "deterrent" measures under international law to stop the Syrian regime's crimes. Russia or China would likely veto any U.N. Security Council resolution sanctioning a Western strike against Syria.