Scores of people were killed, including 13 U.S. servicemen, at the Kabul airport in Afghanistan on Thursday in what appears to be a terrorist attack. 

According to U.S. officials, a suicide bomb went off at the airport’s Abbey Gate, followed by an attack by gunmen and then a second blast at a nearby hotel. Hundreds of Afghan citizens had been camped out there waiting to be evacuated.

Capt. William Urban of the U.S. Central Command said in a statement that 13 U.S. soldiers were killed, while 18 others were injured. The Wall Street Journal reported that 90 Afghan citizens were also killed while 143 others were injured. 

U.S. officials have attributed the attack to an offshoot of the Islamic State, who took credit in a report on its news agency. Marine Corp. General Frank McKenzie told reporters that more attacks are expected.

It marks the deadliest day for the U.S. military in Afghanistan since 2011 and came days before the deadline for the U.S. withdrawal from the war-torn country.