Syria's president may see the Tomahawk attack as a 'slap on the wrist' in the absence of a major strategic shift.
Secretary of State says Moscow failed to live up to a chemical weapons agreement.
Moscow had its S-400 missile system in range of the strike.
While Trump stopped short of calling on Assad to leave office, the comments were his strongest suggestion yet that the United States may be edging toward a stronger stance against Assad.
"American policy is based on creating chaos in different parts of the world and creating conflicts among states. This is not new," Syria's President Bashar al-Assad said.
Russia suggested President Donald Trump had no clear strategy in Syria after the U.S. leader said an apparent chemical attack changed his views on Syrian President Bashar al-Assad.
Secretary of State Rex Tillerson and U.S. Ambassador to the U.N. Nikki Haley said the U.S. was no longer interested in pursuing regime change in Syria.
President Assad has strengthened his position with likely fiercer battles to come despite the deadly siege of Aleppo.
"There is absolutely no justification whatsoever for the indiscriminate and savage brutality against civilians."
Those leaving Aleppo would head for Idlib province to the west of the city.
President Assad’s forces now control more than two-thirds of the city.
The Turkish leader issued a swipe at the U.N. and Russian-backed Syria.
Civilian volunteers say the lack of medical supplies and aid will leave many facing death.
The Syrian army and its allies see a risk that Islamic State will regroup in eastern Syria as it is forced from the Iraqi city of Mosul.