David Cameron's demand for a benefits curb for newly arrived workers from the European Union remains a "core part" of his re-negotiating strategy, Downing Street has said.
The Prime Minister is reported to have warned other European leaders that he is ready to campaign for Britain to leave the EU unless they accept in-work benefits for new arrivals are restricted for four years.
His demands were made in a series of stormy meetings with the European Council president Donald Tusk and commission president Jean-Claude Juncker, according to The Daily Telegraph.
Asked about the report, a No 10 spokesman said: "The issue on the four years remains a core part of our renegotiations. That certainly hasn't changed.
"The Prime Minister has always been clear that we don't rule anything out. His focus is very much on re-negotiating the best possible deal for the UK and, once those re-negotiations have been completed, taking that to the British people in a referendum."
Mr Cameron's demand for a benefit curb has always been seen as the most difficult element of his re-negotiation plan, with Mr Tusk warning it will be "very, very difficult" to reach agreement at this month's Brussels summit.
The Prime Minister is continuing his tour of EU capitals with a visit to Sofia, to meet his Bulgarian counterpart Boyko Borissov and president Rosen Plevneliev.
A No 10 spokesman said that it was part of the continuing renegotiation process.
"There isn't text book that you can pull off the shelf which gives a clear guide as to exactly how this is done. We are working our way through this with our colleagues and partners across the EU," the spokesman said.