"We have reached the moment when the world must see justice done", Haley said.
Richard Feinberg of the University of California, San Diego, who led Latin America policy in the Clinton White House, called the change in plans a "shocking abandonment of US leadership in our own hemisphere" and said it "leaves a leadership vacuum that others will rush to fill".
United States officials told Reuters that Washington was weighing a multinational military response.
"Meetings are ongoing, important decisions are being weighed even as we speak", she said.
What has worldwide reaction been?
Asked whether Russian President Vladimir Putin bears responsibility for the alleged chemical attack, Trump responded, "He may".
Earlier Monday, U.S. Defense Secretary Jim Mattis said the United States is not ruling out military action against Syria. Any attack would mark just the second time that the US would deliberately targeted Assad's military.
Since 2012, Israel has struck inside Syria over 100 times, mostly targeting suspected weapons' convoys heading for the Lebanese militant group Hezbollah, which has been fighting alongside Syrian government forces.This Syrian airbase was used by the Iranians in the past to launch drones over Israeli airspace, and its proximity to Lebanon has raised concerns over its use in providing Hezbollah access to advanced weaponry.
Britain's permanent representative Karen Pierce said the situation today was worse than that during the Cold War because then there was no such flagrant disregard of the universal prohibition against chemical weapons.
Saturday's suspected poison gas attack took place in a rebel-held town amid a resumed offensive by Syrian government forces after the collapse of a truce.
Following the alleged attack, Syria and Russian Federation reached an evacuation deal with the Jaish al-Islam rebels, who up until now have been holding Douma. The White House announced Tuesday that he would do so.
One year ago this month, Trump ordered dozens of cruise missiles to be fired at a Syrian air base after declaring there was no doubt Assad had "choked out the lives of helpless" civilians in an attack that used banned gases. The missile strikes did little long-term damage to Syrian government forces and Assad's position has only become stronger with Iranian and Russian support.
The actions so far of the United States and other Western countries have told Assad that "at the end of the day he's going to be allowed to retake the country and survive politically", he said.
2015: UN-OPCW Joint Investigative Mechanism in Syria is established to identify individuals or entities behind chemical weapons attacks.
Syria and Russian Federation have offered to coordinate with the authorities concerned over the inspection visit.
The OPCW did not immediately respond to a request for comment.
The OPCW's fact-finding mission for Syria was established in 2014 to confirm chemical weapons use, but it does not have the mandate to establish who is responsible.
Instead, they have in recent investigations gathered blood samples from victims and interviewed witnesses outside Syria.
Fighting between the army and rebels escalated and by August 2012 the conflict had become a full-blown civil war.