The militant had been holed up in the same building in which Lebanese army troops had battled the al Qaeda-inspired militants who were hiding there on Sunday.
''We were conducting a normal security operation and then it seemed obvious there was some unusual movement in the building,'' the security source said.
Security forces then tried to negotiate with the militant to give himself up. ''Just as he came out of the apartment, he blew himself up,'' the security source said.
The building was empty and no security forces were wounded in the attack.
Reuters DS GC1910