A drone flew over the Russian trade delegation's villa on an island outside Stockholm early Saturday and dumped paint and an unknown sticky substance onto the building before flying away, police said.

No one was hurt and the villa wasn't evacuated, according to Ola Osterling, press secretary for the Stockholm regional police.

The trade delegation's staff spotted the drone and saw it drop a container with the paint and unidentified substance around 5:30 a.m. local time, Osterling said. They then called Stockholm regional police.

Investigators took samples of the substance for analysis and opened a case into vandalism and harassment, Osterling said. Officers didn't see the drone but interviewed the staff who witnessed it. It wasn't clear who was behind the incident.

The Lidingö island houses foreign embassies and their satellite offices and residences, such as the trade delegation's villa, Osterling said.