Algeria siege: British hostage 'was executed'
British hostage Kenny Whiteside was "lined up" and shot dead in the Algerian siege, his brother has said.
Three British hostages have been confirmed dead while efforts continue to locate a further three Britons believed killed. Five of the names are unconfirmed by the Foreign Office.
David Cameron has pledged help to "find and dismantle" the network responsible.
The first confirmed victim - Paul Thomas Morgan - was named in a statement by the family released via the Foreign Office, while Mr Whiteside and another man - Garry Barlow - have been named as victims by relatives.
A fourth Briton believed to have been killed has been named locally, in Perthshire, as Carson Bilsland.
The prime minister told MPs the UK would "work closely with the Algerian government to learn the lessons of this attack and to deepen our security co-operation".
"And we will contribute British intelligence and counter-terrorism assets to an international effort to find and dismantle the network that planned and ordered the brutal assault," he said.
"We must work right across the region."
A raid by Algerian troops on Saturday ended the four-day siege at a gas plant near the town of In Amenas, in the east of the country, that is thought to have left as many as 48 hostages dead.
Bob Whiteside said he had been told by one of his brother's colleagues that he had been "executed as the Algerian army went in the first time - they just lined up four and shot them".
In an interview with BBC News, Mr Whiteside said his family had found out about his brother's death through a Facebook message from the Algerian colleague.
"We were not given any official information and it was through Facebook, of all things, that we found out of Kenny's demise."
He said police had visited him on Sunday night to confirm the death of his 59-year-old brother, who lived with his wife and two daughters in Johannesburg, South Africa.
Families of other British victims have also been paying tribute to them.
Mr Morgan's mother, Marianne, 65, and his 36-year-old partner, Emma Steele, described the 46-year-old as "a true gentleman, a family man".
"He very much loved his partner Emma, his mum, brothers and sister, of who he was very proud," the statement said.
"We are so proud of him and so proud of what he achieved in his life."
The family of Garry Barlow described "a loving, devoted family man" who "loved life and lived it to the full".
In a statement, the widow of the 49-year-old father-of-two, from Liverpool, said he was "very proud of his family, as they were of him".
She said his family was "totally devastated" by the death of Mr Barlow, a system supervisor for BP at the In Amenas plant.
Carson Bilsland, originally from Bridge of Cally, near Blairgowrie in Perthshire, was described as a former member of the British speed skiing team and an adventure sport enthusiast.
John Macpherson, who had worked with Mr Bilsland as a ski instructor at Glenshee, described him as a "very vibrant character" whose loss was a great shock.
A UK-based Colombian is also thought to be dead.
Twenty-two British survivors have been flown back to the UK and reunited with their families.
Speaking in the Commons, Mr Cameron said that in Algeria, as in Somalia, "terrorist activity has been fed by hostage ransoms and wider criminality".
"To date, the threat it poses has been to these North African states themselves and, of course, to Western interests in those states.
"But as it escalates it is also becoming a magnet for jihadists from other countries who share this poisonous ideology."
Algerian Prime Minister Abdelmalek Sellal said 37 foreigners from eight nationalities were killed during the siege. As many as 48 hostages, including Algerians, are thought to have died in total.
The dead or missing also include workers from the US, Japan, Norway, Malaysia, the Philippines and Romania.
Mr Sellal said 29 militants had been killed and three captured alive.
Algerian officials said the hostage-takers - from six different nationalities - belonged to a new Islamist group formed by a veteran Algerian militant and kidnapper, Mokhtar Belmokhtar, who recently broke from al-Qaeda.
Mauritanian website Sahara Media says he has claimed responsibility for the hostage-taking in a video message.
The video is said to have showed Belmokhtar claiming he was prepared to negotiate with Western and Algerian leaders if French military offensives against Islamists in neighbouring Mali were stopped.
The crisis began on Wednesday when militants attacked two buses carrying foreign workers and Algerians to the remote site in south-eastern Algeria. A Briton and an Algerian reportedly died at the scene.
The militants then took Algerians and foreign workers hostage at the complex, which was quickly surrounded by the Algerian army.
Among the Britons, two of the survivors have been named as Lou Fear, 56, from Louth in Lincolnshire and Allen McCloud, 53, from Plymouth in Devon.
Other freed hostages have been named as Iain Strachan, 38, from Howwood in Renfrewshire; Darren Matthews, from Saltburn-by-the-Sea, Teesside; Mark Grant, 29, from Grangemouth, near Falkirk; Alan Wright, 37, from Portsoy in Aberdeenshire; Peter Hunter, 53, from County Durham; David Murray, 47, from Kirkby in Merseyside; Huw Edwards, 55, from Macclesfield in Cheshire; Martin Johnson, 62, of Todmorden in West Yorkshire; Tony Grisedale, 60, from Workington in Cumbria and Stephen McFaul, 36, from Belfast.