An worldwide fact-finding mission from the Organization for the Prohibition of Chemical Weapons is in Syria and expected to visit Douma.
On Friday night, the US, France and the United Kingdom launched coordinated strikes in Syria as President Donald Trump sought to "punish" his Syrian counterpart Bashar al-Assad for a suspected chemical attack in Douma, Eastern Ghouta, that killed over 70 people.
The US-led strikes were the biggest worldwide attack on President Bashar al-Assad's regime since the start of Syria's seven-year war.
Russian Federation has reacted strongly to the air strikes and warned of "consequences".
Chemical weapons inspectors have not yet been allowed access to Syria's Douma, UK officials said as the Organisation for the Prohibition of Chemical Weapons (OPCW) met to discuss the "alleged use of chemical weapons" in Syria.
An OPCW meeting devoted to the possible use of chemical weapons in Syria is being held in The Hague on Monday. French President Emmanuel Macron spoke with Russian President Vladimir Putin on Friday, hours before the Western missile strikes. According to a Pentagon official, targets were selected that participated in the research, development and deployment of chemical weapons.
The OPCW team will also have to deal with the risk that evidence may have been removed from the site, which lies in an area that has been controlled by Russian military police and Syrian forces over the past week. On Saturday, an OPCW expert group arrived in Syria to investigate the incident.
Trump hailed the predawn strikes that lit up the sky around Damascus and exclaimed "Mission Accomplished" on Twitter.
Regime forces have since entered Douma and declared the entire Eastern Ghouta region around it fully retaken, ending a five-year siege and reclaiming an opposition bastion on the edge of the capital.
The Pentagon said no further action was planned but Washington's envoy to the United Nations, Nikki Haley, warned that the USA was "locked and loaded" should another gas attack occur.
The statement also indicated that ongoing investigations remain confidential.
Waving a huge Syrian national flag and banners saying "No U.S. war on Syria", "U.S. out of the Middle East" and "Money for people's need, NO war", protesters massed at a square at 5:30 p.m. (0130 GMT Sunday) and marched around streets nearby afterward.
A Western draft resolution obtained by AFP at a meeting of the UN Security Council Saturday calls for unimpeded deliveries of humanitarian aid and enforcement of a ceasefire, along with demands that Syria engage in UN-led peace talks. The Syrian government and its ally Russian Federation denied the allegations.
State-run Al-Ikhbariya TV says a second batch of 5,000 security forces deployed in Douma on Sunday.