Britain's Cameron: Prepare for 'bad news' as Algerian hostage crisis unfolds NEW: A Belfast man says his brother had explosives around his neck when he escaped Islamist militants take Algerian and foreign hostages at a gas plant in Algeria British, Norwegian, U.S. and Japanese citizens are among those held hostage "There are still hostages, and there are still terrorists," a senior U.S. official says (CNN) -- British Prime Minister David Cameron warned his compatriots to prepare for "bad news ahead" related to kidnapping of dozens of hostages at a gas facility in Algeria. Nearly 600 workers and four foreign nationals -- two Scots, a Kenyan and a French citizen -- were free by late Thursday after an operation launched by Algeria's military, according to the state-run Algerian Press Service. Some hostages were still presumably being held, and the crisis is far from over. "It is a fluid situation, it is ongoing," Cameron told the Reuters news agency. But I think we should be prepared for the possibility of further bad news, very difficult news, in this extremely difficult situation. The Algerian military operation was over by Thursday evening, according to the Algerian Press Service. At that point, there was no immediate indication as to how many had been killed or injured, how many hostages were still being held, what their condition was or if future action would be taken. The military operation led to numerous casualties, though the exact number wasn't known, APS reported. Cameron acknowledged, in his Reuters interview, that a British citizen "very sadly died." While the Algerian military raid wrapped up on Thursday, a senior U.S. official stressed later that night that more military operations could be coming. "There are still hostages, and there are still terrorists," the official said. So tomorrow is another day. Algerians and foreign workers were taken hostage at the gas plant in Wednesday's assault, apparently in direct response to France's offensive in nearby Mali. The gas field is 60 kilometers (40 miles) west of the Libyan border and 1,300 kilometers (about 800 miles) from the Algerian capital, Algiers. It is not clear whether the hostage-takers wore the suicide vests when they staged the action, another U.S. official said. Nine Norwegian employees of Statoil are unaccounted for, while five Norwegian nationals -- as well as three Algerians -- who work for the company are safe, the company said in a statement. Former hostage Stephen McFaul had plastic explosives strapped around his neck, duct tape over his mouth and rope around his hands, his brother Brian McFaul told CNN from Belfast. McFaul made a break for freedom after the vehicle he was in -- one of several targeted by Algerian fighters -- crashed, with the explosives still around his neck. "The joy was unreal," Brian McFaul said upon hearing his brother was safe. I haven't seen my mother move as fast in all my life, and my mother smile as much, hugging each other ... You couldn't describe the feeling. One of the kidnapped Americans is a Texas man, a family member told CNN. By Thursday night, some Americans had been freed and spoke with family members back home, while others remained unaccounted for, U.S. officials said. 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 said Thursday on state TV. Algerian troops fired on at least two SUVs trying to leave the kidnapping site, Algerian radio said, citing local sources. And an Algerian reporter saw heavy clashes near the site, APS and radio reports said. "There were a number of dead and injured, we don't have a final figure," Said said. An unarmed Predator drone has flown over the plant to gather intelligence, a U.S. official said Thursday. Meanwhile, two oil companies that operated at the site -- BP and Statoil -- are pulling all of their non-essential personnel from Algeria. "Our focus is 100 percent on the safety and welfare of those people and their families, and we are now beginning a staged and planned reduction in non-essential workforce on a temporary basis, pulling them out of the country," said BP Vice President Peter Maher from London's Gatwick Airport, where a chartered flight from Algeria was set to arrive Thursday night. French President Francois Hollande earlier confirmed the presence of French citizens on site but would not say whether any were hostages. Cameron -- who canceled a Friday speech in the Netherlands -- talked with U.S. President Barack Obama about the situation Thursday, according to a Downing Street statement. Before Algeria launched its military operation, U.S. officials urged the Algerians to be cautious and make the hostages' safety their first priority, an Obama administration official said. However, Algerian government officials did not tell their U.S. counterparts in advance about their military raid, according to the official. A senior U.S. official said, at this point, the United States doesn't trust the information it is getting from the Algerians, "because we hear one thing and then we hear something else." There are also fears that the tactics used by the Algerian forces may have put hostages in jeopardy, though the official acknowledged they could have hit even harder. "In all fairness, they could have ended it today," the senior U.S. official said. They haven't used all the severeness they could. They know hostages are left. CNN's Joe Sterling and Greg Botelho wrote this story from Atlanta. CNN's Elise Labott, David Mattingly, Athena Jones, Barbara Starr, Jethro Mullen, Tim Lister and Faith Karimi contributed to this report, as did journalists Peter Taggert from Belfast Said Ben Ali contributed from Algiers.