Two environmental campaigners have boarded an oil rig as it was being towed out to sea in the Cromarty Firth.
Greenpeace activists said they scaled the Transocean rig Paul B Loyd Junior, contracted to BP, on Sunday evening.
They are calling for BP to end drilling for new oil wells.
BP said it shared the protesters' concerns about climate change and was "working every day to advance to a low carbon future".
But it warned: "While we recognise the right for peaceful protest, the actions of this group are irresponsible and may put themselves and others unnecessarily at risk."
Greenpeace said the 27,000-tonne rig owned by Transocean was on its way to the Vorlich field to drill new oil wells operated by BP.
One of those on board the rig, an activist named Jo, told the BBC's Good Morning Scotland programme what she hoped to achieve.
She said: "We are in a climate emergency. This rig is going out to the Vorlich oil field to drill a new hole which will extract 30 million barrels of oil, they hope, when we already cannot afford to burn the oil we've already got in production - it seems a bit foolish so we've come up here to try to stop the rig going out."
She said they intended to stay on board as long as they can but conceded they would only be able to delay the rig's journey for a few days.
"But it's sending a message to these companies and it's also raising awareness with other people. We have to send a message to these companies that it's just not acceptable," she said.
BP said it was working with the rig owner Transocean and the authorities to try to resolve the situation.
Police Scotland said it was working with the operators, Cromarty Firth Port Authority and others in an effort to resolve the situation as "safely as possible".
The Cromarty Firth is a sheltered area of sea, north of Inverness, used for parking oil and gas rigs and platforms when not in use, or when they are undergoing refurbishment.
Last month, Greenpeace activists demanding the company end its oil exploration.