ISIS kills U.S. troops as they prepare to withdraw. Trump said they were already defeated.

The Islamic State has just killed four American troops and wounded three others in northern Syria according to U.S. officials as they were preparing to withdraw from the country.

President Donald Trump made headlines when he declared on Twitter that the terrorist group was already defeated.

“We have defeated Isis in Syria, my only reason for being there during the Trump Presidency,” the president wrote on Twitter on December 19.

The incident is adding new doubt to Trump's claim.

ISIS claimed responsibility for the attack in less than an hour after one of its members wore an explosive vest on a busy restaurant center in a strategically important city controlled by the US-led coalition. Troops were "were killed during an explosion while conducting a routine patrol in Syria today," a released statement read. More than a dozen civilians were also killed.

The attack is the worst loss of life on the US military in Syria since it first went to fight ISIS there in 2015.

The exact date of complete withdrawal isn't known yet but Trump said that it would begin almost immediately.

Trump was briefed on the attack according to the White House but has so far not responded on the matter.

When you check his Twitter account he instead chose to write about all the "walls around the world" and the "radical democrats." Not one word from him.

The Pentagon is also not currently commenting on this story.