About 60 foreign hostages are unaccounted for in the stand-off with Islamist militants, Algeria’s state news service says.
It said more than half the 132 foreigners had been freed, but could not account for the rest.
Special forces have resumed negotiations after the attack launched yesterday at the gas plant deep in the Sahara, it said.
A Mauritanian news site that frequently receives messages from al Qaida linked militants said the hostage-takers had offered to trade two captive Americans for two jailed terror figures in the United States.
One of the two, Omar Abdel Rahman, masterminded the 1993 World Trade Centre bombing.