Mohammad al-Rajali says rebel reports have Khamis Gadhafi as being among 33 troops killed in a NATO strike early Friday on a government operations center in Zlitan.
Officials in the Libyan capital Tripoli could not be reach for comment.
NATO says there has been bombing around Zlitan on Thursday. An alliance spokesman in Brussels said Friday that NATO could not verify the report.
Zlitan is 90 miles (140 kilometers) southeast of Tripoli. Khamis runs Libya's 32nd Brigade, which has been fighting the rebels in Zlitan.