Police in northern Greece have clashed briefly with extreme left protesters outside an international trade fair where the prime minister is hosting the commerce secretary of the United States.

The protesters dispersed quickly from a square by the Thessaloniki International Exhibition Center. Two other demonstrations — one staged by 6,000 pro-communist unionists and one with about 7,000 participants from other trade unions, ended without incident on Saturday night.

But Greek nationalists opposed to the government’s deal to end a name dispute with neighboring Macedonia remained on Thessaloniki’s waterfront.

Police fired tear gas and stun grenades after some of the 6,000 nationalist protesters threw rocks and other objects at officers.

U.S. Commerce Secretary Wilbur Ross spoke at the trade fair before Prime Minister Alexis Tsipras’ keynote address on the economy.