Dawn newspaper reported Wednesday eight bodies of policemen and employees of the water and power development authority had been recovered from fields near the 500 kilowatt Budh Berh Sheik Muhammadi power grid station on the outskirts of Peshawar where the attack occurred Tuesday.
The dead included five utility employees and three policemen who were on guard duty, the report said. Officials said the attackers fired seven rockets that set the facility on fire, and that 13 explosive devices planted at the site also went off.
Power supply in many areas of Peshawar was knocked out for several hours.
A police official told Dawn six power station vehicles and official records also were damaged in the attack.
Another four employees of the power station remained missing and authorities were searching for them.
Pakistan's News International quoted a police official that the attack was carried out by about 40 militants, who managed to enter the facility after blowing up the boundary wall.
Peshawar is the capital of the northwest Khyber Pakhtunkhwa province near the border with Afghanistan, and has been the scene of much militant violence in recent years in which hundreds have died.
Some of the past attacks have come from the Pakistani Taliban, which is independent of the similar group in Afghanistan.
The latest violence, for which there was no immediate claim of responsibility, comes as Pakistan gets ready for general elections on May 11. A civilian government, under a coalition regime led by the Pakistan People's Party, completed its full term of five years last month, a major political milestone as the military has intermittently ruled the country for decades since the founding of Pakistan in 1947.