Sellal said the militants had expected to return to Mali with the foreign hostages.
The four Chinese nationals are thought to have been the only foreign hostages held by the group.
Some foreign hostages were killed when forces raided the southeast Algerian natural-gas facility, called In Amenas, an Algerian government official confirmed.
Four foreign hostages were freed in an Algerian military operation but there were a number of "victims", the official Algerian APS news agency said.
Algerian forces stormed a gas facility to free foreign hostages without warning other governments, leaving leaders in a series of capitals scrambling to get information on their citizens' fates.
On Tuesday afternoon, Chester Zoo announced that a decision had been taken to postpone the trip following news at the weekend that a Nigerian Islamist militant group had killed seven foreign hostages.
BBC: Chester Zoo team on the hunt for new species in Nigeria
Algerian media said that between 30 and 40 Algerian workers had escaped from the Tigantourine facility on Thursday, with Ennahar television saying that 15 foreign hostages were now also safely out of the area.
Foreign workers were among the hostages, but the nationalities of the dead are not known.
"Algeria's not a country that would feel comfortable relying on foreign security forces to help liberate the hostages, and that's because of this deep-seated feeling that there should be no foreign military presence in the country, " said Robert Parks, director of the Centre for North African Studies in Algeria.
The French foreign minister has met the families of many of the hostages to keep them up-to-date.
Russia's foreign ministry confirmed two of its citizens were among the hostages taken between the Cameroonian port of Douala and the port of Malabo in Equatorial Guinea.
The foreign governments insist that no attempt should be made to use force to free the hostages.
Officials suggested this week that some foreign fighters might have been among the rebels involved in the seizing of hundreds of hostages at a Moscow theatre.
After some hours, the French foreign ministry said in a statement that it formally "denied the information that the French hostages had been released".
The UK Foreign Office has refused to confirm the latest figures from Algeria indicating that around 100 out of a total of 132 hostages have been freed.
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