President Gjorge Ivanov said the agreement, which would rename Macedonia as the Republic of North Macedonia, gave too many concessions to Greece.
Macedonian Prime Minister Zoran Zaev has also hailed the deal, which was announced on Tuesday, calling it a "historic solution". After that, Macedonia's parliament would vote on it, and if it is approved, Ivanov's signature would be needed.
Reaction to the news was swift with the EU's High Representative Federica Mogherini and European Union enlargement commissioner Johannes Hahn both issuing statements which congratulated Greece and Macedonia on their "historic agreement". To survive the no-confidence vote, the prime minister needs the full support of his governing bloc and especially of his coalition junior partner, the right-wing Independent Greeks.
He said the deal "benefits (Greece) and the region...with this agreement, we cancel out any attempt to usurp our history".
Macedonian president refuses to approve name deal with Greece
Greek PM Alexis Tsipras also faces opposition at home. After the demise of Macedonia's bid for NATO membership in 2008, the government of then-prime minister Nikola Gruevski - leader of the Macedonian Revolutionary Organisation-Democratic Party for Macedonian National Unity (VMRO-DPMNE) - started to capitalise on the resulting sense of isolation. Earlier this week, following 27 years of tense UN-led negotiations, the countries made an important step towards resolving their dispute over Macedonia's name.
"We lost the country, this is a disaster", 45-year-old lawyer Mila Ivanovska said in Skopje, the Macedonian capital, and began to cry.
The head of Greece's main opposition party is criticizing a deal reached between Greece and Macedonia to end a decades-long dispute over the latter's name, describing it as "deeply problematic".
Tsipras said that the crucial point of the compromise was to differentiate the neighbouring country from the ancient and modern-day Greek province of Macedonia with the geographic qualifier "Northern". This effectively changed Bulgaria's position, which had theretofore ruled out a name that included a geographical limitation. Equally, if the agreement succeeds but the European Union makes no concessions on Greece's debt problems, Tsipras could face a similar fate.
The name dispute has soured relations between the two neighbours since 1991, when Macedonia broke away from the former Yugoslavia. Opponents in Macedonia see any modification of the country's name as a threat to their national identity. The deal includes provisions for labels to be placed on statues erected in Macedonia depicting the likeness of Alexander the Great which make clear they refer to ancient Greek times. Greece's lingering dispute with Macedonia has stood in the way of the latter joining North Atlantic Treaty Organisation and the European Union.
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Japanese news media have reported that officials are seeking a meeting between Prime Minister Shinzo Abe and Kim Jong Un . A US official told AFP that "major military exercises have been suspended indefinitely on the Korean peninsula".