WARSAW (Reuters) - Poland has not yet been able to reach agreement with Britain on its push to curb welfare payments to EU migrants, Polish Prime Minister Beata Szydlo said on Thursday, a further blow to David Cameron’s renegotiations with the 28-member bloc.

Britain's Prime Minister David Cameron shakes hands with his Polish counterpart Beata Szydlo during their meeting in Warsaw, Poland December 10, 2015. REUTERS/Kacper Pempel

The British prime minister has promised to reform Britain’s ties with the 28-member bloc before a membership referendum by the end of 2017 but his welfare demands have proved a problem for eastern European member states.

Opposition to those demands has delayed his quest to get what he calls better terms for Britain, and last week he said he did not expect to meet a deadline for reaching a deal on his proposed reforms at a European Council meeting later this month.

Szydlo said Poland wanted Britain to remain in the European Union and would do everything to support the country but that some issues would need further discussion.

“There are proposals from the British government, which are without discussions acceptable for us,” she told a joint news conference with Cameron in Warsaw after a meeting to discuss the British renegotiation.

“There are issues on which there is not a full agreement between us ... This is, among others, the issue of welfare benefits,” she added.

Szydlo did not answer when asked by a British journalist whether Poland would ever accept Cameron’s proposal for a four-year ban on EU migrants receiving some benefits in Britain.

Poland, a former communist state in eastern Europe, has been one of the main beneficiaries of the EU’s principle of ‘freedom of movement’ since its accession in 2004, with tens of thousands of Poles now working in Britain.

Szydlo’s Eurosceptic government sympathises with the British criticism of the EU and shares London’s opposition to ever-deeper integration. Her Law and Justice (Pis) party are also in the same European Parliament group as Cameron’s Conservatives.

The British leader said the problem of migration flows and the pressure they put on public services needed to be addressed and the pair had agreed to work together to find a solution.

“I believe with the type of political will I have seen here in Poland we can find a way,” he said. “It’s going to take time, but I feel there is the good will to reach an agreement.”

Cameron has said he wants Britain to stay in a reformed EU but will rule nothing out if he cannot get the changes he wants.

In an interview with the Spectator magazine published on Thursday, Cameron said he believed the euro zone crisis and migration crisis risked putting Britons off EU membership in the short term but they may see longer term benefits.

“The short term reaction can be: ‘get me out of here!’,” he said. “The longer-term reaction is: we must find a better way of working with our partners because we share the same challenges.”