President Francois Hollande has said authorities will "do our utmost to find the perpetrators" following the brutal deaths of four people - including three members of a British family - in the French Alps.
Mr Hollande, making his third visit to the UK today, joined David Cameron in pledging to get to the bottom of the tragedy.
Addressing journalists at ParalympicsGB House in Westfield, Mr Hollande offered his sympathy to those affected by the killings.
Speaking through an interpreter, he said: "I expressed my emotion earlier today to the British people in relation to the terrible deaths.
"Both the French and the British family have been impacted by this terrible event and we will do our utmost to find the perpetrators, to find the reasons behind that event.
"Our police are co-operating and everything that is found will be shared."
Mr Cameron said he and Mr Hollande had discussed "all of the key issues", including financial and international matters, but were united in their desire to find those responsible for the deaths.
"We obviously have discussed the tragic case, the terrible killings, of the British family near Annecy," he said.
"Consular staff are working very hard so that we do everything we can to help those poor children.
"We will stay in close contact. All the support that the British Government and the Foreign Office can give to those two children, of course we will make sure they get that help, whether in France or whether there is extra help we need to send to make sure they have everything they need."