David Cameron tonight said he was "deeply saddened" by the death of a British man who was killed in the crash of an airliner in Mali.
It emerged today that the Briton, who has not been named, was among the passengers on board Air Algerie Flight AH5017.
The Prime Minister said: "Thoughts very much with friends and family."
Earlier, a Foreign Office spokesman said: " It is with deep regret that the Foreign and Commonwealth Office confirms the death of a British man onboard Air Algerie flight AH 5017.
"We are providing consular support to his family at this tragic time, and we ask that the media respect the privacy of those grieving."
Mr Cameron has also written to French president Francois Hollande "to send sincere condolences for the loss of so many French citizens", Downing Street said.
Earlier, Mr Hollande said that French soldiers had secured one of the black boxes from the aircraft which went down with the loss of at least 116 people.
It was recovered from the wreckage, in the Gossi region near the border with Burkina Faso, and is being taken to the northern city of Gao, where a French military contingent is based
Terrorism has not been ruled out as a cause of the crash, although officials have said that it is most likely to have been due to bad weather.
"There are, alas, no survivors," Mr Hollande told reporters following a crisis meeting with senior ministers. "I share the pain of families living through this terrible ordeal."
Nearly half of the passengers aboard the flight were French, many due to head on to Europe after arriving in the Algerian capital Algiers from the Burkina Faso capital, Ouagadougou.
Mr Hollande has said that France will spare no efforts to find out what happened.
"There are hypotheses, notably weather-related, but we don't rule out anything because we want to know what happened," the French president said.
Interior minister Bernard Cazeneuve added: "Terrorist groups are in the zone. ... We know these groups are hostile to Western interests."
The MD-83 aircraft, owned by Spanish company Swiftair and leased by Algeria's flagship carrier, disappeared from radar less than an hour after it took off early yesterday from Ouagadougou for Algiers. The plane had requested permission to change course due to bad weather.