New details emerge about how four U.S. military members died in Afghanistan As the coffins of four U.S. service members returned to Dover, Del. Wednesday amid outrage over the government's inability to pay their families death benefits or travel expenses, Fox News has learned new details about the attack in which they died Sunday in Afghanistan. The incident, which occurred in Panjwai district 25 miles west of Kandahar, the spiritual birthplace of the Taliban, is currently under investigation by the U.S. military. Fox News has learned that 13 other service members were also severely injured in the assault. The injured began arriving at Walter Reed National Army Medical Center earlier this week although some were not yet stable enough to move from Landstuhl Regional Medical Center in Germany. Senior U.S. military sources describe the attack as "complex." A Ranger regiment that included 36 troops and a canine unit were attempting to capture a high value target in Panjwai in southern Afghanistan. When the troops arrived at the home, U.S. military officials said, the unit did a typical "call out" asking for those inside to come out. One man appeared. Reports from the battlefield suggest he dropped to his knees and lifted his shirt to show the U.S. forces that he was not wearing a suicide bomb vest. As several members of the Ranger unit moved toward the man to begin questioning him, a woman wearing a suicide vest emerged from the house and blew herself up, killing several members of the unit instantly, along with the dog, and injuring others. Another Afghan male tried to escape from the compound. As U.S. army medics, explosives specialists and others in the unit moved in to help the wounded, 13 improvised explosive devices went off, killing and injuring more U.S. forces. They were the last casualties before the Afghan war entered its 13th year Monday. The four killed were Army Rangers Sgt. Patrick C. Hawkins, 25, assigned to Company B, 3rd Battalion, 75th Ranger Regiment, at Fort Benning, Ga.; Pfc. Cody J. Patterson, 24, assigned to Company B, 3rd Battalion, 75th Ranger Regiment, at Fort Benning, Ga.;1st Lt. Jennifer M. Moreno, 25, assigned to Madigan Army Medical Center, Joint Base Lewis-McChord, Wash., and attached to a joint special operations task force as a Cultural Support Team member; and Special Agent Joseph M. Peters, 24, assigned to the 286th Military Police Detachment (CID), 5th Military Police Battalion, Vicenza, Italy. U.S. military spokesman in Afghanistan Matthew Leas said Wednesday, "At this time, we cannot confirm the details of the operation as there is currently an ongoing investigation, which is standard practice. We can confirm that in addition to the four soldiers killed in action, 13 soldiers were wounded in action, but out of respect for their privacy, will not elaborate on the extent of their injuries.