Members of the U.S. military carry a transfer case covered with an American flag during a dignified transfer for Sgt. Leandro Jasso on Nov. 27 in Dover, Del. (Mark Makela/Getty Images)

Three U.S. service members were killed Tuesday when a roadside bomb detonated next to their vehicle in the embattled province of Ghazni, U.S. military officials said. 

Three other U.S. service members were wounded along with a U.S. military contractor, they added. The survivors were evacuated from the area and are receiving medical attention. The names of the dead and the injured were not immediately released.

Separately, the military said Tuesday that a preliminary review has found that an Afghan commando probably shot a U.S. Army Ranger by accident Saturday during a raid on a compound in a remote part of the country. The U.S. soldier died later that day.

Combined, the deaths bring the number of U.S. troops killed in combat in Afghanistan this year to 13. Five of those deaths occurred this month.

U.S. military officials said the attack Tuesday took place during a military patrol near Ghazni city, which has remained tense and unstable since Taliban forces overran it in August in a four-day siege that left more than 100 people dead and parts of the city in ruins.

Aref Noori, a spokesman for the Ghazni governor’s office, said a joint military operation by Afghan and NATO troops had been underway in a village southeast of Ghazni city Tuesday morning when the bomb struck an armored military vehicle carrying foreign forces.

In the past several weeks, the insurgents also have launched assaults on villages in rural districts of the province that are populated by minority ethnic Hazara Shiites. The attacks sent thousands of residents fleeing to nearby provinces.

Senior U.S. military officials have sought to reassure Afghan forces. Army Gen. Austin “Scott” Miller, the top U.S. officer in the country, took the unusual step of carrying a rifle in the city last week. More typically, a general carries a pistol.

The incident Saturday killed Sgt. Leandro Jasso, 25, in Nimruz province’s Khash Rod district. The operation was somewhat unusual because the coalition said it came against al-Qaeda militants, rather than those of the Islamic State (ISIS), which are more typically targeted.

The U.S. military said in a statement that Jasso and other U.S. and Afghan soldiers were involved in a close-quarters battle with “multiple barricaded al-Qaeda shooters.”

“Sgt. Jasso was killed defending our nation, fighting al-Qaeda alongside our Afghan partners,” Miller said in a statement. “All of us, and through our coalition of 41 nations, recognize the threats posed by groups such as al-Qaeda and ISIS and are determined to fight them here.”

The coalition identified Jasso on Sunday, but had not previously acknowledged the possibility of friendly fire. He was evacuated from the compound, and later died at a military hospital at Camp Dwyer, a coalition installation in neighboring Helmand province.

Earlier in the month, Army Maj. Brent R. Taylor was shot dead in an insider attack in Kabul. Taylor was the mayor of Ogden, Utah, and a member of the Utah Army National Guard.

About 15,000 U.S. troops are deployed to Afghanistan, with most involved in Resolute Support, a U.S.-led NATO mission to train, advise and assist Afghan forces battling the Taliban. A separate counterterrorism mission known as Freedom’s Sentinel also is underway, with U.S. Special Operations troops often partnering with Afghan commandos to target the Islamic State and, occasionally, al-Qaeda.

The total number of U.S. military casualties during the 17-year Afghan war is more than 2,400. The great majority of U.S. forces withdrew by the end of 2014, but those still in the country often are involved in supporting combat situations on the ground as well as by air.

Lamothe reported from Washington.