Nato's secretary general has urged Macedonia to settle a long dispute with Greece over the name of the former Yugoslav republic.
The Nato chief used the most diplomatic language in Greece
Speaking after talks in Athens, Jaap de Hoop Scheffer implied that the onus to compromise rested with Skopje.
Greece has said it will block Macedonia from joining Nato and the EU unless it compromises over its official name.
Officials in Athens fear the former Yugoslavs have territorial designs on Greece's northern Macedonia province.
Speaking in Athens after talks with Greek leaders, Mr de Hoop Scheffer said he wanted consensus among all Nato members on Macedonia's joining the alliance, but pointed out that Greece's stance carried weight on the issue.
"I think we have to realise that Greece is a staunch member of Nato, and aspiring members are not. This is a basic difference," he said.
"I hope that a solution can be found - that would be a big plus - but it has to be made possible."
Mr de Hoop Scheffer also said that Macedonia needed to meet Nato's performance targets to join the bloc.
The Nato chief used the most diplomatic language, but he was left in no doubt that Greece would, if necessary, use its veto at next month's Nato summit in Bucharest to prevent Macedonia joining the bloc, the BBC's Malcolm Brabant in Athens says.
Time is running out for a deal between Skopje and Athens to solve the 17-year-long dispute and the signs are not good, our correspondent says.
Over the weekend, Macedonia rejected five alternative names put forward by the special UN mediator, Matthew Nimitz.
Some analysts fear Nato rejection of Skopje's membership bid could trigger internal trouble between the ethnic Macedonian majority and the Albanian minority in the country.