Flags are being lowered to half-staff at all public buildings in Colorado to honor the victims of the Thursday bombings at Hamid Karzai International Airport in Kabul, Gov. Jared Polis’ office announced. 

President Joe Biden on Thursday indicated the Islamic State group’s Afghanistan affiliate was responsible the attacks, which Pentagon officials say left 13 American service members dead and another 18 wounded.

According to the Associated Press, it was the deadliest day for U.S. forces in Afghanistan since August 2011, when a helicopter was shot down by an insurgent armed with a rocket-propelled grenade, killing 30 American troops and eight Afghans.

In response, Polis ordered flags to half-staff through sunset on Sunday.

That order came in conjunction with a proclamation from Biden also ordering flags to half-staff at public buildings “as a mark of respect for the U.S. service members and other victims killed in the terrorist attack on August 26.”