David Cameron's drive to renegotiate the terms of Britain's membership of the European Union suffered a series of setbacks in meetings with continental counterparts.
The Prime Minister continued his effort to build support for his renegotiation plan in a round of bilateral talks with fellow EU leaders during a Europe-Latin America summit in Brussels.
However he was warned by Belgian Prime Minister Charles Michel that his country had a series of "red line" issues - including free movement of labour - on which it would not compromise.
There was also resistance to elements of his plans from the leaders of Romania, Spain and Finland.
"There can't be any ambiguity: at the end of the process, the result can't be that we dismantle Europe," the Belgian Le Soir news website quoted Mr Michel as saying following their talks.
"For Belgium there are red lines: the principles of free movement and non-discrimination between EU citizens are inviolable.
"Neither can there be any veto given to national parliaments - that would be the end of the European Union."
Mr Michel, who described their discussion as "open and frank", said he could not rule out the prospect that the re-negotiation would end with Britain voting to leave the EU in Mr Cameron's promised referendum.
"I can't rule anything out. But it is the British who have pushed the referendum button. It's democracy and no-one in Europe argues with that. I recognise that, on Europe, British public opinion see things differently to ours," he said.
"But if the British think that it is possible for them to enjoy only the advantages of EU membership while the drawbacks are only for the rest, that will not work."
The Telegraph reported that Spanish prime minister Mariano Rajoy told Mr Cameron that treaty change "can't be done" while Finland's Juha Sipila said he was unwilling to enter a "carousel" of treaty negotiations.
Klaus Iohannis, the Romanian president told Mr Cameron he opposes "discriminatory" measures on benefits.
"No member state is allowed to treat people coming from elsewhere different form its own people," he is reported to have said after the meeting. "It's my best interest to have Romanians treated as European citizens everywhere in the European Union."
Downing Street insisted that the Prime Minister expected to hear "lots of views expressed during this process".
The Prime Minister's spokeswoman said: "The PM is absolutely committed to addressing the concerns of the British people and to working with other leaders to find those solutions."
Number 10 pointed to comments from Mr Iohannis saying that the UK "clearly belongs in the EU" and that he acknowledged that "we need to start a process to separate the right of free movement to that of access to social benefits".
"You have got someone there who shares the Prime Minister's concern about the impact of free movement on social security systems and thinks we should be looking at it," the spokeswoman said.
Mr Rajoy had been clear that he "wants to work with us" on British concerns, she said, but acknowledged: "There are a number of areas that are going to be more challenging than others to solve.
"We don't underestimate this is going to take time and patience."
At a regular briefing with journalists in Westminster, the spokeswoman rejected the assertion that Mr Cameron had been "told to get lost in various different languages" at the Brussels meetings.
"I certainly wouldn't characterise it like you just put it," she told reporters. "He has had the opportunity for good discussions with four more European leaders, many of those expressed their determination to do all they could to keep Britain in the EU and certainly a desire to work with us to find solutions."
Asked whether Mr Cameron was more or less confident of progress on his agenda following the talks, the spokeswoman said: "He is pleased that he has had face to face discussions with four more European leaders and he plans to continue that next week."
The Prime Minister hopes to speak to all 27 other European leaders before the European Council summit on June 25-26, where the UK's concerns are expected to be on the agenda.