Protesters have disrupted work on the 496MW Saint-Brieuc offshore wind farm off France, according to the Prefecture Maritime de l’Atlantique.
Support vessel Arethra was forced to leave the area of the wind farm in order to lower the tension caused by the protests, the Prefecture said.
The protests started around 10am local time on 24 June and included firing distress flares at the vessel, verbal threats to board the Arethra and to sabotage its propulsion system, it added.
The Prefecture said that the protesters also failed to comply with its orders governing the work on the wind farm by approaching within 500 metres of the work and carrying out dangerous manoeuvers.
It mobilised the coastal maritime surveillance boat Trieux, which had maritime gendarmerie on board and the Lion vessel with the French Navy on board.
The protests ended just before midday local time.
The Prefecture said the local gendarmerie are currently carrying out the first hearings of a judicial investigation into the protests.