Two more Greenpeace activists are occupying an oil rig in the North Sea, the organisation said.
The pair are believed to have boarded the rig in the Cromarty Firth at around 4am on Friday.
Campaigners from the environmental organisation have been occupying the structure since Sunday evening.
They have been calling on BP to stop drilling for oil and hoped to stop the drilling rig from reaching the Vorlich oil field.
The latest development follows the arrest of two men – aged 40 and 50 – on Thursday who had been part of a five-day protest at the site.
John Sauven, executive director at Greenpeace UK, said: “Our climbers are back on the oil rig and determined to stay for as long as possible. BP are heading out to drill a new well giving them access to 30 million barrels of oil – something we can’t afford in the middle of a climate emergency.
“We can’t give up and let oil giants carry on with business as usual because that means giving up on a habitable planet and our kids’ future.
“The UK Government has announced a target of net zero greenhouse emissions by 2050 – we have started to enforce it.”
The Transocean PBLJ rig was under contract to BP.
A BP spokesman said: “BP continues to work with Transocean, Police Scotland and all relevant authorities to bring this reckless action by Greenpeace to a safe conclusion.
“BP supports debate, discussion and peaceful demonstration, but the irresponsible actions of this group are putting themselves and others unnecessarily at risk, while ignoring court orders and police action.”