Algerian bomb squads scouring the Ain Amenas gas plant for booby traps said today that they had found "numerous" dead bodies.
A spokesman said they were badly disfigured and hard to identify, so it wasn't clear if they were Algerian or foreign workers.
Algerian commandos stormed the Sahara desert site on Saturday to end a four-day standoff.
The government said all 32 Islamist gunmen had been killed.
But its top spokesman said he feared the hostages' death toll, which was 23 on Saturday, would rise as the special forces searched the plant.
Sonatrach, the Algerian state oil company running the plant with BP and Norway's Statoil, said that the entire refinery had been mined.
It was unclear whether anyone was rescued in Saturday's raid, but seven hostages were killed - the same number the militants said they still held that morning.
Algerian troops twice assaulted the two areas where hostages were being held - first on Thursday, then on Saturday.
"To avoid a bloody turn of events in response to the extreme danger of the situation, the army's special forces launched an intervention with efficiency and professionalism to neutralise the terrorist groups that were first trying to flee with the hostages and then blow up the gas facilities," the Interior Ministry claimed.
In the final assault, the remaining militants killed seven hostages before 11 of them were in turn killed by the soldiers, Algeria's state news agency claimed.
It added that the military launched Saturday's assault to stop a fire started by the Islamists from engulfing the plant and blowing it up.
A total of 685 Algerian and 107 foreign workers were freed over the course of the Algerian army's four-day stand-off with 32 men of six different nationalities.
Around a dozen hostages were still unaccounted for today evening.