Sept. 24 (UPI) -- Four U.S. Marines remain hospitalized after an attack near Hamid Karzai International Airport in Kabul, Afghanistan, last month as service members were evacuating foreign nationals and refugees. The suicide attack by Islamic State-Khorasan Province at the airport's Abbey Gate on Aug. 26 killed 13 U.S. service members and more than 170 Afghan civilians. Nearly a month later, four of the injured Marines remain hospitalized at Walter Reed National Military Medical Center in Bethesda, Md., where 15 service members initially were being treated after the attack, Marine Corps Times reported. The names and units of the hospitalized Marines haven't been released. Johnny Henderson said one of the hospitalized Marines is in very serious but stable condition and the other three are in serious but stable condition.