The Syrian Government and its ally Russia have denied involvement in any such attack.
Responding to Haley's remarks about the plans for new sanctions, Evgeny Serebrennikov, deputy head of the defence committee of Russia's upper house of Parliament, said Moscow was ready for the penalties, according to RIA news agency.
"They are hard for us, but will do more damage to the USA and Europe," RIA quoted Serebrennikov as saying.
In Damascus, Syria's Deputy Foreign Minister, Faisal Mekdad, met inspectors from the global chemical weapons watchdog OPCW for about three hours in the presence of Russian officers and a senior Syrian security official.
The inspectors were due to attempt to visit the Douma site.
Moscow condemned the Western states for refusing to wait for OPCW's findings before attacking.
French President Emmanuel Macron says France wants to launch a diplomatic initiative over Syria that would include Western powers, Russia and Turkey.
Macron, speaking on French television BFM and online site Mediapart, said "we are preparing a political solution" aiming at allowing a political solution for Syria.
He stressed the French diplomacy is able to talk with Iran, Russia and Turkey on one side, and the United States on the other side.
He said "10 days ago President Trump wanted to withdraw from Syria. We convinced him to remain."
Macron added that the Russians are "accomplices" of the use of chemical weapons by the Syrian regime because they blocked the UN Security Council.
Assad told a group of visiting Russian lawmakers that the Western missile strikes were an act of aggression, Russian news agencies reported.
Syria released video of the wreckage of a bombed-out research lab, but also of Assad arriving at work as usual, with the caption "morning of resilience" and there were no immediate reports of casualties.
Russian agencies quoted the lawmakers as saying that Assad was in a "good mood", had praised the Soviet-era air defence systems Syria used to repel the Western attacks and had accepted an invitation to visit Russia at an unspecified time.
Russian Deputy Foreign Minister Sergei Ryabkov said Moscow would make every effort to improve political relations with the West, TASS news agency reported today.
Ryabkov also said Russia would study a UN resolution on Syria proposed by the US, France and Britain, but added that it would be hard to reach a compromise on the issue, TASS reported. It's not known when the resolution would be put to a vote.
- Reuters, AAP, AP
