Police have arrested two Greenpeace activists who had boarded a North Sea oil rig as the environmental group said it was sending its ship Arctic Sunrise to join the protest in defiance of court orders obtained by BP.

The oil firm has taken out injunctions against the ship and the Greenpeace ice-breaker, the Esperanza, forbidding them from supporting a protest on a rig in Scotland’s Cromarty Firth that is now in its sixth day.

BP said: “Given Greenpeace’s repeated interference and reckless actions directed at our lawful business and their continued illegal defiance for court orders and police action, we have issued the injunction as a precautionary measure to protect the safety of people and operations.”

Police have arrested 14 people over the occupation of the 27,000-tonne rig, five of whom have appeared in court over the last three days.

On Friday evening police removed and arrested the latest pair of activists who had boarded the Paul B Loyd Jr rig at dawn and had been locked to a gantry.

Ch Supt George MacDonald, Highlands and Islands divisional commander, said: “Officers returned to the platform around 2pm and, after deploying specialist tactics to access the area, subsequently arrested a man and woman who had been carrying out a continued protest on the rig. They have since been safely returned to shore by boat.

“Three further people were arrested on land earlier in the day in connection with this operation. This brings the total number of people arrested to 14 and enquiries are ongoing.”

The rig is owned by Transocean, a US oil contractor that operated the Deepwater Horizon rig on BP’s behalf. Deepwater Horizon blew up in 2010, killing 11 oil workers and releasing 4m barrels of oil into the Gulf of Mexico.

Greenpeace said court officers served papers on the Arctic Sunrise two hours after it docked in Sunderland en route to the Cromarty Firth. The group said it had no plans at present to send the Esperanza to join the protest.

John Sauven, the executive director of Greenpeace UK, said the Arctic Sunrise had documented some of the damage caused by Deepwater Horizon.

“We won’t be cowed by the oil giant’s legal threats. BP is using every legal means available to stop us, and we’ll be using every peaceful means available to stop them,” he said. “We won’t give up until BP have ditched fossil fuels and fully switched to renewables.”

Greenpeace’s decision to step up the protest will be seen by BP, Transocean and Police Scotland as highly provocative. Transocean secured a Scottish court order on Tuesday ordering Greenpeace and its activists to leave the rig, which the organisation has ignored.

The protest began at 6.30pm on Sunday when three activists boarded the rig, preventing it from travelling out to the North Sea. Two remained on board for 24 hours before being relieved by another pair of activists, who were arrested by police late on Thursday evening.

On Friday morning two activists appeared in court in Inverness charged with disorderly conduct, following appearances earlier this week by three others charged with the same offence. A warrant has been issued for a sixth defendant who has not yet appeared in court.

The five activists who have appeared in court are due to stand trial in August. The charges include that they boarded an oil platform without permission or lawful authority, refused to leave, attached themselves to the platform by tethers and committed a breach of the peace.

Ch Supt George MacDonald, the local police commander, said on Thursday night that the Greenpeace protests could have put people in danger, a message echoed by BP. “The particular nature of this protest on an oil platform within a marine environment made this an extremely complex and challenging operation,” MacDonald said.