Celiz, 32, from Summerville, South Carolina, died of wounds from enemy small-arms fire, according to an Army news release. He'd been conducting operations in support of a medical evacuation landing zone in Zurmat district, Paktia province.
An Afghan security force member was also killed in the incident, and several others were wounded. The attack is under investigation.
Celiz was the second U.S. soldier killed in Afghanistan in five days. On July 7, Army Cpl. Joseph Maciel, a 20-year-old infantryman from California, was killed in an apparent insider attack in southern Afghanistan.
Celiz was assigned to Company D, 1st Battalion, 75th Ranger Regiment, based out of Hunter Army Airfield, Georgia. One of his commanders called him a "national treasure" who led his Rangers with "passion, competence, and an infectiously positive attitude no matter the situation."
"The 75th Ranger Regiment suffered a tremendous loss with the passing of Sgt. 1st Class Chris Celiz," Col. Brandon Tegtmeier, the 75th Ranger Regiment commander, said in a statement. "The Celiz family has been a critical component of our team and their community in Savannah, Georgia.
"He will be greatly missed," Tegtmeier added.
Celiz was immediately treated for his wounds and medically evacuated to the nearest treatment facility, where he died. He was serving as the battalion mortar platoon sergeant and was in the process of reclassifying to the infantry branch.
He was on his fifth deployment with 1st Battalion, 75th Ranger Regiment. Celiz also previously deployed to Iraq in 2008 and Afghanistan in 2009.
Celiz was a "great Ranger leader" who will be sorely missed, Lt. Col. Sean McGee, commander of 1st Ranger Battalion, said in a statement.
"He had an incredibly positive attitude that inspired Rangers throughout the formation," McGee said. "Sgt. 1st Class Celiz led from the front and always put himself at the decisive point on the battlefield. He was a loving husband and father, and he and his family have been an important part of the fabric that represents 1st Ranger Battalion and the Savannah community."
In 2013, Celiz was selected to serve with the 75th Ranger Regiment as a combat engineer. He was assigned to Headquarters and Headquarters Company, 1st Battalion, 75th Ranger Regiment, where he served as the battalion master breacher and engineer.
In March 2017, he was assigned to Company D, where he served as the mortar platoon sergeant.
Celiz joined the Army in September 2007. He completed Basic Combat Training and Advanced Individual Training as a combat engineer at Fort Leonard Wood, Missouri.
His first assignment was as a combat engineer and team leader with Company E, 2nd Battalion, 7th Cavalry Regiment, out of Fort Hood, Texas. He was transferred to be a team leader with Company C, 4th Brigade Special Troops Battalion, also at Fort Hood, and then to Fort Stewart in Georgia, where he served as a Sapper squad leader and platoon sergeant with the 530th Engineer Clearance Company, 92nd Engineer Battalion.
Celiz has been posthumously awarded the Meritorious Service Medal, Bronze Star Medal and the Purple Heart, the Army release states.
His other awards and decorations include the Joint Service Commendation Medal; Army Achievement Medal with four oak-leaf clusters; the Meritorious Unit Citation Medal; the Army Service Ribbon; the Ranger Tab; the Sapper Tab; Combat Action Badge; Parachutist Badge; and the Marksmanship Qualification Badge Expert-Rifle.