Algerian hostage crisis at a gas facility in the desert, where Islamist militants were holding foreign hostages, has yet to be resolved, the UK says.
The UK Foreign Office said the “terrorist incident” near In Amenas was “ongoing”.
Algerian state media said four hostages and several militants were killed when troops backed by helicopters attempted to free them on Thursday afternoon.
The militants had claimed to be holding 41 foreigners. At least four were freed but the fate of many others is unknown.
Algeria has yet to give precise casualty figures from the rescue attempt.
The state-run APS news agency cited local officials as saying two Britons and two Filipinos were killed. Two others, a Briton and an Algerian, died on Wednesday when the militants ambushed a bus that was taking foreign workers at the facility to the local airport.
A spokesman for the militants told the Mauritanian ANI news agency that 35 hostages and 15 militants had been killed by helicopter gunfire in Thursday’s operation.
Norwegian Foreign Minister Espen Barth Eide said: “Parts of the plant are under Algerian authorities’ control, and other parts are not. This information is changing by the hour.”
The indications on Thursday night were that the military element of the operation had concluded, and that it had moved to the search phase.
But there are now some unconfirmed reports that a small group of militants and hostages remain, possibly near the gas compressor at the main gas plant.
It had always been reported that hostages were being held at different locations.
Algerian hostage crisis at a gas facility in the desert, where Islamist militants were holding foreign hostages, has yet to be resolved
UK government sources said they were trying to establish the fate of as many as 20 British people and were bracing themselves for multiple casualties.
Japanese officials were meanwhile cited as saying by the Kyodo news agency that at least 14 Japanese nationals were still missing. At least three managed to escape.
Japan’s Chief Cabinet Secretary, Yoshihide Suga, expressed “deep regret” at the actions of the Algerian security forces and its foreign ministry summoned the Algerian ambassador.
Norwegian Prime Minister Jens Stoltenberg said the Algerian officials had said “they felt they had no choice but to go in”.
Norway said eight of its nationals were currently unaccounted for. One is being treated at a hospital in In Amenas, while four escaped unharmed.
French Interior Minister Manuel Valls said two French workers were safe. It was unclear if another two were involved, he added.
The Irish government confirmed that one of its citizens was free. Five Americans had survived and left the country, US officials told ABC News.
APS said about 600 local workers had been freed in the raid, but many of those were reportedly allowed to leave on Wednesday by the militants.
The militants said they had seized the foreigners in retaliation for France’s military intervention in Mali, where its forces have been battling Islamists since last week.
Algerian Communications Minister Mohand Said Oubelaid said the militants were intent on “destabilizing Algeria, embroiling it in the Mali conflict and damaging its natural gas infrastructure.”
Algerian officials said the group was operating under orders from Mokhtar Belmokhtar, a senior commander of al-Qaeda in the Islamic Maghreb (AQIM) until late last year.
The In Amenas gas field is operated by the Algerian state oil company, Sonatrach, along with the British oil company BP and Norway’s Statoil.
It is situated at Tigantourine, about 40 km (25 miles) south-west of the town of In Amenas and 1,300 km (800 miles) south-east of Algiers.
Ecuador has accused the UK of making a “threat” to enter its embassy in London to arrest WikiLeaks founder Julian Assange.
Julian Assange, 41, took refuge at the Ecuadorian embassy in June to avoid extradition to Sweden, where he faces questioning over assault and rape claims, which he denies.
Ecuador says a decision on his bid for political asylum will come later.
The UK Foreign Office says it can lift the embassy’s diplomatic status to fulfill a “legal obligation” to extradite Julian Assange.
The WikiLeaks website published a mass of leaked diplomatic cables that embarrassed several governments, particularly the US, in 2010, and Julian Assange says he fears that Sweden will pass him on to the American authorities.
A number of police officers are outside the Ecuadorian embassy, in Knightsbridge, where some of Julian Assange’s supporters have also gathered.
Demonstrators also protested outside the British embassy in Ecuador’s capital. Images from Quito showed protesters holding signs saying “We are sovereign, not colonies” and a union jack being stepped on.
Ecuador has accused the UK of making a "threat" to enter its embassy in London to arrest WikiLeaks founder Julian Assange
At a news conference in Quito on Wednesday, Ecuador Foreign Minister Ricardo Patino said a letter from the UK government had been delivered through a British embassy official.
“Today we received from the United Kingdom an express threat, in writing, that they might storm our embassy in London if we don’t hand over Julian Assange,” he said.
“Ecuador rejects in the most emphatic terms the explicit threat of the British official communication.”
Ricardo Patino said such a threat was “improper of a democratic, civilized and rule-abiding country”.
He added: “If the measure announced in the British official communication is enacted, it will be interpreted by Ecuador as an unacceptable, unfriendly and hostile act and as an attempt against our sovereignty. It would force us to respond.
“We are not a British colony.”
A Foreign Office spokesman said the UK remained “determined” to fulfill its obligation to extradite Julian Assange.
“Throughout this process we have drawn the Ecuadorians’ attention to relevant provisions of our law, whether, for example, the extensive human rights safeguards in our extradition procedures, or to the legal status of diplomatic premises in the UK,” the spokesman said.
“We are still committed to reaching a mutually acceptable solution.”
Police have so far been unable to detain Julian Assange for breaching the terms of his bail as he is on diplomatic territory.
The law Britain has informed Ecuador it could use in the case is the Diplomatic and Consular Premises Act 1987.
It allows the UK to revoke the diplomatic status of an embassy on UK soil, which would potentially allow police to enter the building to arrest Julian Assange.
On Monday, Ecuador’s President Rafael Correa said a decision would be made this week after he held a meeting with his advisers.
Ricardo Patino told reporters an announcement on Julian Assange’s bid for political asylum would be issued on Thursday, at 07:00 local time (13:00 BST).
In 2010, two female ex-WikiLeaks volunteers accused Julian Assange, an Australian citizen, of committing sexual offences against them while he was in Stockholm to give a lecture.
Julian Assange claims the sex was consensual and the allegations are politically motivated.
He says he is concerned he may be sent later to the US to face espionage charges.
In June, judges at the UK’s Supreme Court dismissed his final appeal against extradition to Sweden.
An offer by Ecuador to allow Swedish investigators to interview Julian Assange inside the embassy was rejected.
UK letter to Ecuador
Foreign Minister Ricardo Patino said the letter from the UK to Ecuador stated: “You need to be aware that there is a legal base in the UK, the Diplomatic and Consular Premises Act 1987, that would allow us to take actions in order to arrest Mr Assange in the current premises of the embassy.
“We sincerely hope that we do not reach that point, but if you are not capable of resolving this matter of Mr. Assange’s presence in your premises, this is an open option for us.”
It went on: “We need to reiterate that we consider the continued use of the diplomatic premises in this way incompatible with the Vienna Convention and unsustainable and we have made clear the serious implications that this has for our diplomatic relations.”
Queen Sofia of Spain has cancelled her visit to the UK for Queen Elizabeth’s Diamond Jubilee because of disputes over Gibraltar.
A Spanish government statement said it was “hardly appropriate” for Queen Sofia, 73, to attend a lunch on Friday.
The UK and Spain have been in dispute over fishing rights off Gibraltar, a UK territory which Spain also claims.
Spain has also protested over a visit to Gibraltar by Queen Elizabeth’s son Prince Edward and his wife Sophie.
Prince Edward and the Countess of Wessex are to visit Gibraltar on 11-13 June as part of the celebrations to mark the 60th anniversary of the Queen’s reign.
Queen Sofia of Spain has cancelled her visit to the UK for Queen Elizabeth's Diamond Jubilee because of disputes over Gibraltar
Spain continues to claim sovereignty over Gibraltar, which has been ruled by Britain since 1713 under the terms of the Treaty of Utrecht.
Queen Sofia’s husband, King Juan Carlos, had already declined his invitation to the lunch at Windsor Castle on Friday.
He is recovering from surgery last month after he fell and broke his hip while hunting elephants in Botswana.
In 1981, the Spanish royal couple declined an invitation to Prince Charles’ wedding to Diana, Princess of Wales because they planned to visit Gibraltar as part of their honeymoon.
And a visit by Princess Anne to Gibraltar in 2009 sparked an official complaint from the Spanish government.
An additional cause of unhappiness for the Spanish royal household is the fact that the British regimental band of Gibraltar will be performing at the Diamond Jubilee, reports the Spanish news agency Efe.
A spokesman for the UK Foreign Office told the AFP news agency: “The visit was a private commitment and we don’t comment on private visits.”