LONDON - British Prime Minister David Cameron warned ministers on Sunday they would have to support staying in the European Union or leave his government, newspapers reported.
It came after signs of rebellion within his Conservative party over a planned referendum on whether Britain should remain in the 28-member bloc.
"If you want to be part of the government you have to take the view that we are engaged in an exercise of renegotiation to have a referendum and that will lead to a successful outcome," Cameron told reporters, according to the Guardian, Telegraph and other newspapers.
"Everyone in government has signed up to the programme set out in the Conservative manifesto," he said on the sidelines of the G7 summit of world leaders in Germany.
Cameron has pledged to campaign for Britain to remain in the EU after renegotiating the country's ties with the bloc ahead of the vote, planned by 2017.
But he is vulnerable to resistance from the eurosceptic wing of his Conservative party, which has a slim majority in parliament.
A group of more than 50 lawmakers have said they will lead calls for Britain to leave the EU unless he secures major concessions from Brussels.
The group, Conservatives for Britain, is poised to front the campaign to leave unless Cameron secures major changes such as regaining control over free trade powers and British laws.
Since his re-election last month Cameron has pressed ahead on securing reforms, undertaking a whirlwind tour of European capitals to seek support for reforms like making it harder for EU migrants to claim benefits in Britain.