The Pentagon identified on Wednesday three U.S. troops killed in Afghanistan a day earlier as two Special Forces soldiers and a special tactics airman who was assigned to work alongside the Army.

Army Capt. Andrew Ross, 29, and Army Sgt. 1st Class Eric Emond, 39, were members of the 3rd Special Forces Group, the Pentagon said in a statement. They were killed along with Air Force Staff Sgt. Dylan Elchin, 25, a combat controller whose job included directing aircraft overhead to support soldiers on the ground.

The deaths bring the number of U.S. troops killed in combat in Afghanistan this year to 13, drawing new attention to the longest war in American history. Five of those deaths occurred this month.

A bomb exploded near their vehicle in Ghazni province, an area of Afghanistan that has been embattled for months, drawing renewed attention from the U.S. military. Three other U.S. service members were wounded, along with a U.S. military contractor.

Emond had served the longest of the three killed, with more than 21 years split between the Marine Corps and, later, the Army, according to a biography released by his current service. A married father with three children, he grew up in Boston and was on his seventh deployment. He was posthumously awarded the Purple Heart, his second, for his injuries.

Ross was a native of Lexington, Va., a town in the Shenandoah Valley. He was on his second deployment and leaves behind a wife and parents.

“Andrew and Eric were invaluable members and leaders in 3rd Special Forces Group and the Special Operations community,” said Col. Nathan Prussian, a commanding officer. “Our most heartfelt condolences go out to the families of these brave men.”

Elchin deployed in August as part of an Army Special Forces team and was engaged to be married. He graduated from Hopewell High School in Pennsylvania and enlisted in the Air Force in August 2012 as a combat controller. After completing training, he was assigned to the 26th Special Tactics Squadron at Cannon Air Force Base in New Mexico.

"Dylan had an unusual drive to succeed and contribute to the team. He displayed maturity and stoicism beyond his years, and was always level-headed, no matter the situation,” said Lt. Col. Gregory Walsh, commander of the 26th Special Tactics Squadron. “Our thoughts and prayers go out to Dylan’s family, fiancé, and friends. He will be sorely missed, but never forgotten.”