A soldier from Harford County who was serving in Afghanistan died Saturday during an operation against Islamic State militants in Afghanistan.

Staff Sgt. Mark R. De Alencar died of “injuries sustained when his unit came in contact with enemy forces using small arms fire during combat operations,” according to a statement from the Department of Defense.

His body was returned to the United States at Dover Air Force Base in Delaware on Monday evening.

De Alencar, a 1998 Joppatowne High School graduate, was a member of the Army’s Special Forces.

The 37-year-old Edgewood resident was part of the 1st Battalion, 7th Special Forces Group (Airborne) and was assigned to Eglin Air Force Base in Valparaiso, Fla., officials said.

De Alencar and Afghan troops were operating in the Nangarhar province in the eastern part of the country.

He had been working with Afghan soldiers, fighting insurgents affiliated with the Islamic State, or ISIS, according to the NATO-led Resolute Support Mission working with Afghan security forces.

“On behalf of all U.S. Forces-Afghanistan, I offer our deepest condolences to the family and friends of our fallen comrade,” said Gen. John W. Nicholson, commander of U.S. Forces-Afghanistan and Resolute Support, in a statement Sunday.

Jansen Robinson, an Edgewood resident and a member of the Harford County Board of Education, is related to De Alencar through marriage — his niece, Natasha, is De Alencar’s wife.

He said Natasha De Alencar also graduated from Joppatowne High. He described the couple as “soul mates.”

He said they had five children and had been together for about 15 years.

“They shared a life together,” Robinson said. “She was his rock, he was her rock, so she’s taking it pretty hard.”

The Army reported a combat death over the weekend, but did not release De Alencar’s name until Monday afternoon, after his family had been notified.

News of his death began to filter out Sunday via social media. De Alencar’s name and photograph were posted on the Joppatowne High School Alumni Facebook page Sunday. Several people wrote tributes and left condolences for his family.

Kilo Mack, principal at Edgewood High School, was a teacher at Joppatowne when De Alencar was a student. Mack was overcome during a phone interview Monday after seeing a photo of De Alencar in his Army uniform, which had been posted online.

“He was a good kid,” he said.

De Alencar was a member of the football team, Mack said.

“I remember when he joined the Army and him being very happy and excited,” he said. “I recall him seeing this as an opportunity to do something better for himself and with his life.”

daanderson@baltsun.com