Trump's letter to congressional leaders cites the rationale he gave publicly Friday night when he announced that the USA and allies Britain and France were firing missiles into Syria in response to an alleged poison gas attack on Syrian rebels near Damascus the previous week.
There is also the risk that evidence may have been removed from the site, which lies in an area of the town that has been controlled by Russian military police and Syrian forces for the past week.
The OPCW inspectors met Syria's deputy foreign minister, Faisal Mekdad, for about three hours on Sunday in the presence of Russian officers and a senior Syrian security official, Reuters reported.
"There's every reason to believe that the goal of the attack on Syria was to obstruct the work of the OPCW inspectors", the statement read. President Bashar Al Assad's government and its ally Russian Federation deny there had been a chemical attack, and western powers claim they already had proof.
Among the sites reportedly hit overnight Friday was the Scientific Studies and Research Centre, a facility that has played a key role in Syria's chemical weapons program since the 1970s.
Doctors at the hospital where suspected victims were treated told reporters on the tour that none of the patients that night had suffered chemical weapons injuries - they were asphyxiated by dust and smoke in a bombardment.
Medical aid groups and the White Helmets rescue organisation have said such statements - already aired on state television in recent days - were made under duress.
The president tells lawmakers that he acted to "promote the stability of the region, to deter the use and proliferation of chemical weapons, and to avert a worsening of the region's current humanitarian catastrophe". "But it was the world saying that we've had enough of the use of chemical weapons". "There is broad-based worldwide support for the action we have taken", May said.
"On the intelligence collected by our services, and in the absence to date of chemical samples analyzed by our own laboratories, France considers, beyond possible doubt, a chemical attack was carried out against civilians at Douma. and that there is no plausible scenario other than that of an attack by Syrian armed forces", the report said.
Jeremy Corbyn, leader of the main opposition Labour Party, has questioned the legal basis for Britain's involvement.
In France, the conservatives, the far-left and the far-right have all criticised the strikes.
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