The Lebanese army says it is in final phase of campaign to defeat Fatah al-Islam.
Eid said one of the rockets struck near one of the reservoirs, causing a fire but it was quickly put out.
The power station was shut down after the attack.
Witnesses reported that there were fierce clashes between the military and fighters still holed up inside the camp on Thursday morning.
“The fighting will continue until this [Fatah al-Islam] phenomenon is eliminated,” an official said.
Last week, Lebanese troops stormed a hideout of Fatah Islam fighters in the camp, killing eight of them, according to the news agency.
General Michel Suleiman, Lebanese army commander, has vowed to continue the battle saying it was a “fight against terrorism” and “a battle of dignity and national sovereignty”.
In a speech during Wednesday’s Army Day, he called the military deaths in the Nahr al-Bared “great sacrifices”.