Greek protesters have clashed with riot police while a historic deal to end a 27-year name dispute was signed.
The demonstration came as the foreign ministers of Greece and Macedonia signed a preliminary accord to rename the country the Republic of North Macedonia.
A woman was hit on the head by a rock and a man was treated for breathing problems during the clashes.
The trouble broke out when about 500 demonstrators waving Greek flags tried to approach the signature ceremony on the banks of Lake Prespa.
But they were surrounded by police near the small village of Pisoderi, about 16 miles from the ceremony.
Riot police blocked the rural road leading to the lake, while others on mountain slopes threw stun grenades and tear gas at the crowd.
The authorities said about 5,000 people took part in the protest against the agreement.
One protester said: “We are fighting for the land of our fathers. We are not backing down.”
Since 1991, Athens has objected to its neighbour being called Macedonia because it has its own northern province of the same name, which in ancient times was the cradle of Alexander the Great’s empire
At the fishing village of Psarades, where the deal was signed, priests tolled the local church bell in a sign of mourning.
Greek Prime Minister Alexis Tsipras said the agreement would heal wounds between the two countries.
He said: “This is a brave, historic and necessary step for our peoples.
“We are here to heal the wounds of time, to open a path for peace, fraternisation and growth for our countries, the Balkans and Europe.”
Macedonia’s Prime Minister Zoran Zaev said: “Our two countries should step out of the past and look to the future.
“Our peoples want peace… we will be partners and allies.”