Inspectors' lack of access to Douma has left unanswered questions about the April 7 attack that prompted a military response by the U.S. and two allies.
U.N. Ambassador Nikki Haley indicates that the sanctions will be aimed at sending a message to Russia for enabling the government of Bashar Assad.
But Syrian allies Russia and Iran call the use of force by Western allies a "military crime" and "act of aggression" with the potential to worsen a humanitarian crisis.
President Trump condemns a "mindless CHEMICAL attack" in Syria that killed women and children, calls the Syrian president an "animal," and threatens unspecified consequences.
On Monday, a series of three coordinated bombings targeting landmark hotels in Baghdad killed at least 36 people and wounded 71, according to The New York Times. Also Monday, Iraqis hung Saddam Hussein's cousin and former aide Ali Hassan al-Majeed --aka "Chemical Ali" -- for crimes against humanity, largely for his role in the mass killing of Iraqi Kurds in 1988.