(ATHENS) - Greece on Friday warned Macedonia again that it would not support its entry into the European Union and NATO unless both states agree to break a 15-year deadlock on the tiny state's official name.

"There can be no invitation to participate in the same alliance without a mutually acceptable solution," Greek Prime Minister Costas Karamanlis told parliament. "No solution means no invitation," he said.

Greece refuses to recognise the former Yugoslav republic by its chosen name, Macedonian Republic, because it is the same as the northern Greek province of Macedonia, and has threatened to block its bid to join NATO and the EU.

Macedonia wants to join the defence alliance at a NATO summit in April.

On Tuesday, senior UN mediator Matthew Nimetz made a confidential proposal to both governments to resolve the dispute, which he said took into account "the historical sensitivities of the people involved."

A document leaked to Greek daily To Vima on Thursday identified five name suggestions: Constitutional Republic of Macedonia, Democratic Republic of Macedonia, Independent Republic of Macedonia, New Republic of Macedonia and Republic of Upper Macedonia.

The name would be used in passports, treaties and Macedonia's relations with international organisations, said the document which the Greek government later confirmed as authentic.

On Thursday, Athens said the UN proposal "has elements that could be accepted under certain circumstances" but proposed certain changes to the text without specifying the modifications it seeks.

"The neighbouring state...must go its own share of the distance so that we can reach a mutually acceptable solution," Karamanlis said.

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