The threat of a U.S. attack comes just as U.N. inspectors in Syria have begun a probe into the chemical allegations. On Monday, the inspectors met with Syrian victims and collected samples to determine if nerve agents were used. The visit was initially delayed after the inspectors’ convoy came under sniper fire. A U.N. spokesperson said Secretary-General Ban Ki-moon still believes the inspectors can make a proper assessment, even though five days passed before they were allowed entry.

Farhan Haq: “Despite the passage of a number of days, the secretary-general is confident that it will be able — that the team will be able to obtain and analyze evidence relevant for its investigation of the 21st of August incident at Ghouta in Damascus. The team will complete its scientific analysis as soon as possible. And the mission will seek to reconstruct an evidence-based narrative of the alleged incidents and other information in accordance with its guidelines.”

If confirmed, the attack in Ghouta would mark the world’s worst chemical weapons strike since 1988, when Iraq’s Saddam Hussein gassed thousands of Kurds in Halabja with U.S. complicity.