"A small group of Liberation Tigers of Tamil Eelam (LTTE) terrorists had fixed explosive devices designed to set off automatically on the fuel storage tanks of the Kelanitissa power station," the defence ministry said in a statement.
No one was injured by the blasts at the power station and two burning fuel storage tanks were quickly extinguished.
State radio quoted police as saying several people were being questioned after the attack, which came exactly one month after suspected members of the LTTE set off a massive explosion in the city's business district, killing 18 people and wounding more than 100.
There was no comment from the LTTE on the latest incident. It denied responsibility for last month's blast.
"Security forces and the Ceylon Electricity Board (CEB) officials took prompt action to douse the fire. Terrorists have failed in their attempt to destroy the power station," the defence ministry statement said.
The Defence Ministry said the authorities had re-started all the turbines at the plan. The area around the station had been sealed off as a precaution soon after the fire, and the authorities prevented people from entering or leaving the city.
Colombo has been under tight security since last month's rebel attack which damaged three hotels and several other buildings, including the twin-tower World Trade Centre. Elsewhere, at least six policemen were killed in an attack by rebels in eastern Sri Lanka on Friday, police officials said.
The LTTE is fighting for a separate homeland for minority Tamils in Sri Lanka's north and east. The government says more than 50,000 people have died in the war that began in 1983.
- Reuters, ColomboReuse content