"Two commanders... And three soldiers were killed today," army spokesman Miloud Zouai was quoted as saying, adding that they had been advancing in a southern district of the city when the explosion occurred.
Yesterday, Zouai had said an officer had been killed by a mine in Benghazi, and three other people wounded.
Benghazi, cradle of the 2011 revolution that overthrew and killed dictator Moamer Kadhafi has been the site of regular fighting between forces loyal to the government and armed groups for more than a year.