PODGORICA, Montenegro (AP) — An official in Montenegro says unidentified people have burned a NATO flag, just days after the small Balkan nation was invited to join the alliance amid opposition from Russia.

Cetinje Mayor Aleksandar Bogdanovic said Monday that the flag was brought down from a pole at the town's entrance. He described the incident as "an absolutely inappropriate act."

Many in Montenegro, which has strong historic and cultural ties to Russia, remain opposed to NATO membership partly because the alliance bombed the country in 1999 while it was still part of a union with Serbia.

Pro-Russia opposition groups are planning an anti-NATO rally on Saturday. They are demanding a national referendum on the issue.