President Donald Trump announced Friday that the U.S., France and Britain together launched military strikes in Syria to punish President Bashar Assad for his alleged use of chemical weapons against civilians and to deter him from doing it again.

Loud explosions lit up the skies over the Syrian capital, as Trump announced the airstrikes.

In an announcement from the White House, 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 international banned chemical weapons.

The decision to strike, after days of deliberations, marked Trump’s second order to attack Syria; he authorized a barrage of Tomahawk cruise missiles to hit a single Syrian airfield in April 2017 in retaliation for Assad’s use of sarin gas against civilians.