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Prime Minister David Cameron and German Chancellor Angela Merkel have spoken by phone and agreed progress has been made in Britain's renegotiation with the EU.

Number 10 said both leaders saw there was genuine goodwill across Europe for Mr Cameron's aims, but accepted there was work to do to find solutions.

A spokesman said they also discussed migration and the Syria conference they will co-host in London next week.

The UK is to hold an in-out referendum on EU membership by the end of 2017.

Mr Cameron has pledged to secure a better deal for the UK in the European Union as a prelude to the referendum, in which voters will be asked whether they want to stay in the EU or leave.

There has been speculation that the PM could call the poll as early as June this year if he gets the backing of the EU's other 27 leaders for his reform demands at a summit in February.

Downing Street also said that while discussing migration during their call, both Mr Cameron and Mrs Merkel agreed that a strong external European border and close co-operation with Turkey were vital.

And they agreed that the Syria conference had "the potential to deliver a substantial increase in both financial and practical support for refugees that would help them to stay in the region".

On Monday, Mr Cameron held talks on the EU with his Irish counterpart Enda Kenny.

Mr Kenny said his personal view was that a deal was possible in February but "he couldn't speak for the other countries around the table".

David Cameron's four main aims for renegotiation

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Economic governance : Securing an explicit recognition that the euro is not the only currency of the European Union, to ensure countries outside the eurozone are not disadvantaged. The UK wants safeguards that it will not have to contribute to eurozone bailouts

: Securing an explicit recognition that the euro is not the only currency of the European Union, to ensure countries outside the eurozone are not disadvantaged. The UK wants safeguards that it will not have to contribute to eurozone bailouts Competitiveness : Setting a target for the reduction of the "burden" of excessive regulation and extending the single market

: Setting a target for the reduction of the "burden" of excessive regulation and extending the single market Immigration : Restricting access to in-work and out-of-work benefits to EU migrants. Specifically, ministers want to stop those coming to the UK from claiming certain benefits until they have been resident for four years

: Restricting access to in-work and out-of-work benefits to EU migrants. Specifically, ministers want to stop those coming to the UK from claiming certain benefits until they have been resident for four years Sovereignty: Allowing Britain to opt out from further political integration. Giving greater powers to national parliaments to block EU legislation

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