CNN — Reporting on militants' seizure of workers at a natural-gas complex in eastern Algeria has been a special challenge, in part because outside journalists need a visa and accreditation before they can enter the country.
Access to live information from the Sahara Desert facility -- which British Prime Minister David Cameron this week noted was "one of the most remote places in the world" and about "18 hours by road from the capital, Algiers" -- is hard to come by, and conflicting accounts have emerged about the hostages and other aspects of the story.
Here is a look at what CNN has reported from official sources; what CNN has reported from other news media; and some unanswered questions:
WHAT OFFICIAL SOURCES SAY
Initial attack on Wednesday
-- The incident began when militants attacked workers who were traveling from In Amenas gas field to the In Amenas Airport early Wednesday, Algerian Interior Minister Diho Weld Qabilyeh told Algerian state television. Two people, an Algerian and a Briton, were killed in that attack, according to Algerian and British officials.
-- After security forces accompanying the workers returned fire, the militants went to the gas installation itself and took hostages, Qabilyeh told Algerian state television.
-- The remote gas field, about 37 miles west of the Libyan border and about 800 miles from the Algerian capital, Algiers, is run by "a joint venture of the Algerian national oil company Sonatrach, (Britain's) BP and (Norway's) Statoil," according to BP.
Initial hostage situation
-- The militants, equipped with AK-47 rifles, reportedly put explosives-laden vests on some of the hostages, a U.S. State Department official said.
-- While Algerian media reports indicated that militants initially had hundreds of hostages, including dozens of foreign workers, CNN doesn't have from official sources clear information on the number and the nationalities of the people who have been held.
-- Officials from the United States, the United Kingdom, Norway, France, Malaysia, Japan and Ireland have said their nationals were among those involved.
Algerian military attacks; more casualties; some hostages escape
-- On Thursday, Algerian forces attacked the militants as they were preparing to move the hostages in vehicles, Algerian Communications Minister Mohamed Said told state television.
-- Thursday's military operation left an unspecified number of people dead and injured, Said told state television.
-- One French citizen was killed and three others were saved in the operation to free hostages, the press office of the Ministry of Foreign Affairs in Paris said Friday.
-- However, since Wednesday, some people have been freed or have escaped. Ireland's government confirmed that one of its citizens, Stephen McFaul, escaped Thursday.
-- McFaul made a break for freedom after a vehicle he was in -- one of several targeted by Algerian fighters -- crashed, with his captors' explosives still around his neck, his brother Brian McFaul told CNN from Belfast.
-- Before Thursday's military raid, some hostages had disguised themselves to escape, according to Regis Amoux, chief executive of the CIS catering firm that had 150 workers who were freed.
-- The United States on Friday was evacuating between 10 and 20 people, a U.S. defense official told CNN. They will be taken to U.S. facilities in Europe, the official said, and the condition of those who are injured will be assessed.
-- BP said Friday that a "small number of BP employees" are still unaccounted for, while Statoil said the fate of eight of its employees at In Amenas was still uncertain. Nine other Statoil workers who were at the plant are safe, it said.
-- By Thursday night, some Americans had been freed and had spoken with relatives back home, while others remained unaccounted for, U.S. officials said.
-- A State Department official told CNN Wednesday that the abductors are demanding that members of their group who are being held prisoner elsewhere be released and sent to northern Mali. U.S. State Department spokeswoman Victoria Nuland said Friday that the United States will not negotiate a prisoner exchange with the militants. CNN has not confirmed whether any Americans still were being held.
WHAT CNN HAS REPORTED, CITING OTHER NEWS MEDIA
Number of dead
-- Twelve hostages have been killed since the Algerian military launched a ground operation on Thursday, the official Algerian news agency said, quoting a security source.
-- State-run Algerian Radio cited an official source as saying that the major military raid that was launched Thursday was over, but that there was "ongoing activity at various locations" near the plant.
Number of hostages
-- Hundreds of people, including hundreds of Algerian workers and 132 foreign workers, were taken hostage Wednesday, according to the state-run Algerian Press Service. CNN has not independently confirmed the numbers.
-- By Friday, 650 hostages have been freed by the Algerian military, according to the state-run Algerian Press Service. Of the 132 foreign workers taken, 100 were released, the agency said. CNN has not independently confirmed the report.
-- The Al-Mulathameen Brigade initially said that 41 "Westerners, including seven Americans, (as well as) French, British and Japanese citizens have been taken hostage," the Mauritanian News Agency and Sahara Media report.
Islamist militants claim responsibility
-- The Al-Mulathameen Brigade, which is associated with al Qaeda in the Islamic Maghreb, claims responsibility for the attack, according to media in the region.
-- A spokesman for Al-Mulathameen told media in the region that the militants claimed to have carried out the operation because Algeria allowed French forces to use its airspace in attacking Islamist militants in Mali. (However, a U.S. official told CNN that the operation's sophistication suggests that it likely was planned well in advance of France's Mali action.)
-- How many people were taken hostage?
-- How many people have been killed?
-- Is the attack directly related to the fighting in Mali, as the militants claim?