"We will not allow this without the approval of the Greek people, which is through elections or a referendum," Panos Kammenos, leader of the nationalist Independent Greeks party and defence minister in the government of Prime Minister Alexis Tsipras, told an emergency press conference.

"The agreement is a poor one. I do not accept it and will attempt to block it," should the deal be put to a vote in parliament in several months, Kammenos said.

The main opposition New Democracy party also rejects the deal, but Tsipras, who controls 145 seats in the 300-seat parliament, could still get it approved with the help of lawmakers from smaller parties who have voiced support.

Greece and Macedonia in June signed a historic preliminary agreement to rename the small Balkan nation the Republic of North Macedonia, ending a row that has poisoned relations between the two neighbours since 1991.

The agreement is expected to be put to Greece's parliament after a referendum and constitutional revision in Macedonia by the end of the year.

In exchange for the name change, Greece will drop its objections to Macedonia joining the European Union and NATO.

Kammenos' participation in a government that seeks to end one of the world's longest diplomatic disputes is threatening his party's political survival.

He has already lost two lawmakers in parliament and several of his party members say they have received threats over the agreement, especially after the Independent Greeks refused to abandon the government in a vote of censure last month.

Over the weekend, Kammenos said he would leave the government "if and when the time comes" to ratify the agreement.

Athens had for years objected to its neighbour being called Macedonia because it has a northern province of the same name, which in ancient times was the cradle of Alexander the Great's empire -- a source of intense pride for modern-day Greeks.

Several protests have been held in Greece and Macedonia against the agreement, which has raised strong objections among hardliners in Skopje too.

Macedonia President Gjorge Ivanov last month refused to sign the deal after it was approved by the country's parliament.

Another vote is scheduled in Skopje this week, one that Ivanov no longer has the power to stall, having exercised his one-time veto option.