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”.