'Military operation' at Algeria hostage site where Belfast man held
A military operation is ongoing at a gas facility in Algeria where several hostages, including a Belfast man, are being held the Foreign Office has said.
Media reports say some hostages and Islamist militants have been killed.
There has been no official confirmation of any deaths. Some hostages are still being held, according to local sources quoted by the Reuters news service.
Earlier, the family of the Belfast man being held appealed for his release "as a matter of urgency".
The 36-year-old is being held along with other foreign nationals.
The kidnappers attacked and occupied the complex on Wednesday, after killing a Briton and an Algerian.
On Thursday, a number of hostages, both Algerian and foreign, escaped, according to media and officials.
Details of the escape and the numbers involved remain unclear, but some 30 to 40 Algerians and 15 to 20 foreign nationals were reported to have escaped.
The militants earlier said they were holding 41 foreign nationals.
Algerian troops have surrounded the facility.
In a statement read by West Belfast MP Paul Maskey, the family said: "We are all very concerned about his welfare and want to see him released to us as a matter of urgency, free from harm.
"Our thoughts are with him and all the other captives."
The Belfast man, who is travelling on an Irish passport, is being held along with British, Japanese, US, French and Norwegian nationals.
Irish Prime Minister (Taoiseach) Enda Kenny also called for the man and the other hostages to be freed.
"We demand the immediate release of this hostage and all the other hostages," he said.
Algerian Interior Minister Daho Ould Kabila said the militants wanted to leave the country with the hostages, but he had refused to let them go.
"We reject all negotiations with the group, which is holding some 20 hostages from several nationalities," he told reporters late on Wednesday.
Mr Kabila added that the kidnappers were Algerian and operating under orders from Mokhtar Belmokhtar, a senior commander of al-Qaeda in the Islamic Maghreb (AQIM) before late last year, when he set up his own armed group after apparently falling out with other leaders.
Dozens of Algerian workers were said to have been released earlier.
Mr Kabila said a heavily armed "terrorist group" had attacked a bus carrying workers from In Amenas at about 05:00 (04:00 GMT).
The gas field is operated by the Algerian state oil company, Sonatrach, along with the British oil company BP and Norway's Statoil.
It is located about 1,300km (800 miles) south-east of Algiers, and about 60km (37 miles) west of the Libyan border.
The attackers were repelled by police who had been escorting the bus, but a Briton and an Algerian national had been killed, Mr Kabila said. Two other British nationals, a Norwegian, two police officers and a security guard were also hurt in the fire-fight, he added.
Afterwards, the militants drove to the gas facility's living quarters and took a number of Algerian and foreign workers hostage.
They were being held in one wing of the living quarters, which the security services and army had surrounded, Mr Kabila said.
Early on Thursday, British Foreign Secretary William Hague confirmed that a Briton had died and that "a number" of others were being held hostage.
He described the killings as the "cold-blooded murder of people going about their business".
A worker told France's Le Figaro newspaper the captors had mined the facility and demanded food, water and vehicles.
Mr Kabila said nearby border crossings had been closed as a precaution and that the foreign ministry was in contact with diplomats from the hostages' countries.
UK Foreign Secretary William Hague confirmed the captives included "a number of British nationals", adding: "This is therefore a very dangerous situation."
He said the UK government was working "around the clock" to resolve the crisis.
There are conflicting reports about the motives behind the attack.
Earlier the AFP news agency quoted one worker as saying the militants had demanded the release of 100 Islamist prisoners currently detained in Algeria. Another report said they wanted France to end its military operation in Mali.
Militant groups have vowed to avenge France's military intervention in Mali, where its forces have been battling Islamists linked to AQIM for the past week. Algeria has been allowing French aircraft to use its air space.