Uncertainty surrounds the fate of those at the In Amenas gas plant in Algeria, following a military operation to free hundreds of workers held hostage by militants.
Algerian forces gained control of part of the facility and some hostages were released.
There are also unverifiable reports that dozens of people have been killed and injured, while many others have managed to escape.
Near the Libyan border, In Amenas is operated by Algeria’s state gas firm, British Petroleum and Norway’s Statoil.
Although the UK has complained that it was not informed of the plan, Algeria says it had to act quickly.
Algerian Communications Minister Mohamed Said Belaid said: “The operation has enabled us to neutralise an important number of terrorists and to free a significant number of hostages. But unfortunately some people have been killed and injured. For the moment, we do not have definitive figures. We will communicate the details as soon as we have them.”
Details of who was behind the attack and why are also sketchy.
Media in the region has reported veteran jihadist Mokhtar Belmokhtar led the siege and that it may be a retaliation for Western intervention in Mali.