(CNN) -- Two days after Islamist militants abducted an undetermined number of hostages -- including Westerners -- at a gas plant in a remote section of Algeria, "ongoing activity at various locations" was continuing, a British official said Friday. It was not clear whether that activity represented "mopping up and checking" or "something more active" being carried out by Algerian forces against the abductors, the official told CNN. Algerian forces launched their operation upon noticing the hostages being moved toward "a neighboring country," where kidnappers could use them "as a means of blackmail with criminal intent," Algerian Communications Minister Mohamed Said told state television on Thursday.
@highlight
British official says there is "ongoing activity at various locations" near gas plant in Algeria
@highlight
British Prime Minister David Cameron warned there could be "bad news ahead"
@highlight
British, Norwegian, U.S. and Japanese citizens are among those held hostage
@highlight
"There are still hostages, and there are still terrorists," a senior U.S. official says
Officials from Norway, the United States, @placeholder and Britain said some of their nationals were among the hostages.