Trump said the U.S.is prepared to sustain pressure on Assad until he ends what the president called a criminal pattern of killing his own people with internationally banned chemical weapons.
Syrian air defense forces targeted an Israeli F-16 fighter jet that was involved in the attack with over 25 anti-aircraft missiles.
The U.S., Great Britain and France fired 105 missiles at three sites in Syria early Saturday morning local time, Lt. Gen. Kenneth McKenzie, director of the joint chiefs of staff, said Saturday at the Pentagon.
It was the first time in 30 years that an Israeli jet was lost in a combat situation and led to an extensive retaliation by Israel with additional strikes against both the Syrian missile batteries and Iranian military targets in the war-torn country.
"A combined operation with the armed forces of France and the United Kingdom is now under way".
More: Russia just blamed Britain for Syria chemical attack. In Damascus, the president's seat of power, hundreds of residents gathered in Omayyad Square, many waving Syrian, Russian and Iranian flags.
Emphasising that the strikes are directed at the Syrian regime, Mattis said in conducting these strikes, the U.S. has gone to great lengths to avoid civilian and foreign casualties.
Johnson tweeted Saturday that he welcomed the news of the military strike against major chemical weapons facilities in Syria in concert with "our USA and French allies".
NATO Secretary General Jens Stoltenberg in a statement backed the strikes, saying they "will reduce the regime's ability to further attack the people of Syria with chemical weapons". "If they give excuses to Iran, Tel Aviv and Haifa will be destroyed", cleric Ali Shirazi said on Thursday according to the semi-official Fars news agency. "This aggression is created to compensate for the defeat of the terrorists" in Eastern Ghouta, an area recently recaptured by Syrian government forces, Iran's foreign ministry said.
"So we've got to take the fight to the Russians and the Iranians, they still haven't paid no real price for this support".
A number of strikes on targets in Syria have been attributed to Israel. The first air strike ordered by Trump occurred in April previous year.
The Assad regime moved its aircraft and some military equipment inside Russian bases for protection, but what about the Iranians?
The army statement was released soon after the leader of Lebanon's militant Hezbollah group said the airstrike that killed seven Iranians was a "historic mistake".