Prime Minister David Cameron meets European leaders in Latvia Friday to start talks that he admits will not be easy on renegotiating Britain’s ties with the EU ahead of a referendum by 2017 on leaving the bloc.

Prime Minister David Cameron meets European leaders in Latvia Friday to start talks that he admits will not be easy on renegotiating Britain's ties with the EU ahead of a referendum by 2017 on leaving the bloc.

Ahead of his first foreign trip since retaining power at this month's general election, he said that by "working together", European countries could "improve the EU as a whole".

"Today I will start discussions in earnest with fellow leaders on reforming the EU and renegotiating the UK's relationship with it," Cameron said in comments released by his Downing Street office.

"These talks will not be easy," he added before a summit in Riga on ties between the European Union and six former Soviet states.

"But by working together in the right spirit and sticking at it, I believe we can find solutions that will address the concerns of the British people and improve the EU as a whole."

Cameron has promised a referendum on whether Britain should leave Europe by the end of 2017. He backs staying in as long as Britain can secure a string of reforms which he has yet to spell out.

Legislation paving the way for the referendum is expected to be published next Thursday, the day after Queen Elizabeth II reads out the government's legislative program at the state opening of parliament.

Cameron says that changes to EU treaties are necessary to secure the changes he wants.

These include controlling migration by making it harder for EU migrants to claim state benefits in Britain, opting out of the EU's commitment to "ever closer union" and handing some powers back to national parliaments.

European Commission chief Jean-Claude Juncker has said he is ready to work with Cameron for "a fair deal" but insists key EU principles such as freedom of movement are non-negotiable.