The 29-year-old Frenchman arrested over the fatal shooting of three people at Brussels' Jewish Museum, has admitted to the killings, authorities said.
Mehdi Nemmouche is said to have admitted to the shooting in a video recording he was carrying while arrested in France.
"(In the video) he states that he committed the attack in Brussels against the Jews," Belgian federal prosecutor Frederic Van Leeuw said at a press conference.
More top news
Mr Osborne said he is "not the person to provide the unity my party needs".
David Cameron is to meet leaders of other EU states for the first time since the referendum vote for Brexit.