BENGHAZI, Libya — The top rebel military commander was killed Thursday, and members of his tribe greeted the announcement with gunfire and angry threats. The violent outburst stirred fears that a tribal feud could divide the forces struggling to topple the Libyan dictator, Col. Muammar el-Qaddafi.

The leader of the rebels’ provisional government, Mustapha Abdul Jalil, announced Thursday evening without providing details that unnamed assassins had killed the commander, Gen. Abdul Fattah Younes, and two other officers.

General Younes, a former officer and interior minister in the Qaddafi government, had long been a contentious figure among the rebels, some of whom doubted his loyalty. He had been summoned to Benghazi for questioning by a panel of judges, and members of his tribe — the Obeidi, one of the largest in the east — evidently blamed the rebel leadership for having some role in the general’s death.

The specter of a violent tribal conflict within the rebel ranks touches on a central fear of the Western nations backing the Libyan insurrection: that the rebels’ democratic goals could give way to a tribal civil war over Libya’s oil resources. Colonel Qaddafi has often warned of such a possibility as he has fought to keep power, while the rebel leaders have argued that their cause transcends Libya’s age-old tribal divisions.