SKOPJE, Macedonia - The European Union's foreign policy chief on Thursday added her voice to a string of western officials urging the people of Macedonia to vote in a referendum on a deal with Greece that could enable the former Yugoslav republic's NATO and EU accession.

Speaking in the capital, Skopje, Federica Mogherini said Macedonians "hold the key to the future" of their country and should participate in the Sept. 30 vote on changing the country's name to "North Macedonia."

"You cannot afford to stay silent and miss the opportunity to express yourselves on what kind of future you want for your country," Mogherini said.

Turnout is important because just over 50 per cent of the 1.8 million registered voters must cast their ballot for the referendum to be valid. Polls indicate that while most Macedonians would back the deal, turnout might fall just short of the threshold.

The main opposition conservatives oppose the deal, but have advised supporters to vote according to their conscience in the referendum.

"The doors of the EU are open for you," Mogherini told reporters after talks with Macedonia's centre-left Prime Minister Zoran Zaev. "Together we can achieve a lot, for all of our people, for our prosperity, for our security, for our stability. You have an historic opportunity in your hands."

Western governments are particularly keen to get the tiny landlocked country into NATO, as that would expand the alliance's presence in the Balkans and diminish Russian influence.

U.S. Assistant Secretary of State for European and Eurasian Affairs Wess Mitchell visited Skopje earlier Thursday, while U.S. Defence Secretary Jim Mattis is expected on Monday.

Mitchell offered "heartfelt and profound" support to Macedonia, noting that the final decision lies with voters.

"But America also has a stake in the western Balkans, of seeing stability and prosperity in a very import region," Mitchell added after talks with Macedonian Foreign Minister Nikola Dimitrov in Skopje.

The referendum will seek approval of a June agreement with Greece aimed to resolve a bitter 27-year dispute between the two Balkan neighbours, and end Greek objections to the country joining NATO and the EU.

Greece argues that Macedonia's current name implies claims on its own adjoining province of Macedonia, and on ancient Greek culture. Macedonia denies that.

Zaev spoke at the European Parliament earlier Thursday and said his country is ready to grasp its "historic moment" and change its name.

Conceding that the name change "will be not an easy decision" for Macedonians, Zaev added that it offered "a once in a lifetime opportunity and we will not miss that opportunity."

At a Pentagon briefing earlier this week, Defence Secretary Mattis told reporters he was concerned about alleged acts of "mischief" by Russia to try to block Macedonia's path to NATO membership.

Russia denies claims of interference, but openly opposes NATO expansion eastward.

News from © The Associated Press, 2018