The long-serving monarch named his successor, Haitham bin Tariq Al Said, who was sworn in as sultan Saturday. Under Qaboos, the tiny Middle Eastern state took on an outsize role in regional diplomacy.
The soldiers were killed when their vehicle hit a roadside bomb planted by the Taliban in Kandahar province. Two other U.S. troops were wounded in the attack.
Iranian media quoted the military as saying human error led to the attack. The foreign minister blamed "US adventurism." Missiles struck the plane just after it took off from Tehran.
Administration officials say Iranian Gen. Qassem Soleimani was killed to prevent "imminent attacks." They're being questioned about what "imminent" means.
Video footage and the locations of key Iranian military facilities lend credence to the idea that the jetliner carrying 176 people was accidentally shot down.
As investigators learn more about what happened to a Ukrainian International Airlines flight which crashed in Tehran, a growing body of online evidence suggests it was shot out of the sky.