(CNN) -- Confusion surrounds the fate of potentially dozens of hostages held at a gas plant deep in the desert as Algerian forces continue activities against their Islamist militant abductors.
A reportedly bloody raid by Algerian forces launched Thursday is over, state-run radio cited an official source as saying -- but there is "ongoing activity at various locations" near the plant, which "some of the hostage-takers are still using as a hideout."
The British Foreign Office said the incident "remains ongoing" Friday, two days after the attackers first struck.
It was not clear whether the activity represented "mopping up and checking" or "something more active" being carried out by Algerian forces against the abductors, a British official told CNN.
It also remains unclear how many hostages have been killed or injured, and how many are still held.
Officials from Norway, the United States, Japan and Britain have said their nationals are among those unaccounted for. A Briton was one of two people confirmed killed Wednesday.
Relatives of workers at the besieged In Amenas plant are braced for bad news following chaotic reports as Algerian forces launched their operation Thursday.
Prime Minister David Cameron's warned late Thursday of "bad news" ahead. Cameron is to address parliament in London Friday morning.
Algeria faces tough questions from the governments of kidnapped nationals over its handling of the crisis amid fears that hostage safety is not being put first.
Japan's Vice-Minister Shunichi Suzuki summoned the Algerian ambassador Friday to express Tokyo's concern, the Japanese foreign ministry said.
Japan's Prime Minister Shinzo Abe is cutting short his South Asia trip to return home to deal with the crisis, his office said.
"There is so much conflicting information on safety of the hostages," Chief Cabinet Secretary Yoshihide Suga told reporters in Tokyo. "Safety of 14 Japanese citizens still remains unknown."