President Donald Trump notified Congress on Saturday of the US missile strikes on Syria days after the event, warning ominously of further actions "as necessary."
In a letter addressed to House Speaker Paul Ryan and Senate president pro tempore Orrin Hatch, Trump gave details on the missile strike on the Shayrat military airfield, launched in retaliation for an apparent chemical attack.
US warships in the Mediterranean fired 59 Tomahawk cruise missiles around 3:40 am Syria time (late Thursday in Washington, 0040 GMT Friday) at the airfield located near Homs in central Syria.
US intelligence indicated "that Syrian military forces operating from this airfield were responsible for the chemical weapons attack on Syrian civilians in southern Idlib Province, Syria, that occurred on April 4," Trump wrote.
"I directed this action in order to degrade the Syrian military's ability to conduct further chemical weapons attacks and to dissuade the Syrian regime from using or proliferating chemical weapons, thereby promoting the stability of the region and averting a worsening of the region's current humanitarian catastrophe."
Trump wrote that he "acted in the vital national security and foreign policy interests of the United States, pursuant to my constitutional authority to conduct foreign relations and as commander in chief and chief executive.
He then added that the United States "will take additional action, as necessary and appropriate, to further its important national interests."
Trump said that he was writing to keep Congress informed "consistent with the War Powers Resolution," a 1973 measure mandating the president to notify Congress of military action.
The Tomahawks targeted aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defense systems and radars, the Pentagon said.
Trump responded via Twitter on Saturday to critics complaining that the airfield's landing strip was undamaged after the missile attack.
"The reason you don't generally hit runways is that they are easy and inexpensive to quickly fix (fill in and top)!" he wrote.