US, British and French "naval and air assets" took part in the strikes, which US defence chief James Mattis said employed more than twice the amount of munitions used in American strikes in Syria previous year, in which 59 Tomahawk missiles were fired.
Syrian state TV said the US, UK and France had launched attacks and said anti-aircraft units had responded.
"We condemn in the strongest terms the use of chemical weapons", Mr Stoltenberg said.
Some U.S. media had said Washington was confident Assad had also used sarin on April 7.
Syria's air defenses have shot down 13 missiles in the Kiswah area south of Damascus, SANA state television reported.
Secretary of Defense Jim Mattis said at a press conference on Friday night that double the amount of weapons were used compared with the strike in April 2017, which consisted of 59 Tomahawk missiles.
Mattis was expected to voice those concerns in Thursday's meeting at the White House, according to U.S. officials.
Describing the strike as a deterrent, Trump said the U.S. would maintain pressure on Syria until the Assad regime suspends use of chemical weapons.
He first made clear that he meant to launch new attacks in a series of tweets earlier this week, issuing warnings against not only Syrian President Bashar al-Assad but also Russian Federation and Iran.
Unlike the 2017 strike when US officials alerted Russian Federation that missiles were incoming, the United States and its allies did not alert Moscow of the impending attack Friday, Dunford said. In April 2017, Mr. Trump ordered a strike of almost 60 Tomahawk missiles that destroyed a Syrian air base days after Assad used sarin gas in an attack that killed dozens of civilians, many of them children.
Meanwhile, the Organisation for the Prohibition of Chemical Weapons (OPCW) says experts are travelling to Syria and will start investigations on Saturday.
Top Senate Democrat Chuck Schumer is calling the airstrikes appropriate, but said "the administration has to be careful about not getting us into a greater and more involved war in Syria". Other nations should step in, Trump said.
Russian foreign ministry spokeswoman Maria Zakharova said last week "We call upon. members of the worldwide community to seriously consider the possible consequences of such accusations, threats and especially action [against Syria]".
"We're again confident that both Syria had responsibility in this chemical weapons attack, but we also hold Russian Federation responsible for their failure to stop chemical weapons attacks from taking place", said White House press secretary Sarah Sanders.
"America does not seek an indefinite presence in Syria under no circumstances", he said.
"This massacre was a significant escalation in a pattern of chemical weapons use by that very bad regime", Trump said on Friday.
British Prime Minister Theresa May said in her country Saturday, according to Reuters, that the allied response was "not about intervening in a civil war". Another US ally, Germany, said on Thursday they would not participate in military action in Syria.