Thunberg, who became the face of young climate activists worldwide after staging weekly protests in front of the Swedish parliament in 2018, has this year been detained by police or removed from protests in Sweden, Norway, and Germany.

Video footage showed Thunberg, wearing a badge with the slogan “Oily Money Out” standing calmly as two police officers spoke to her. One was seen holding her arm. Still images showed her being searched and placed in the back of a police van.

Thunberg had been protesting outside the InterContinental Hotel in Mayfair where the Energy Intelligence Forum was hosting a gathering of oil and gas industry leaders.

She and dozens of others locked arms, obstructing entrances. Police warned the protesters before moving in to detain them.

London’s Metropolitan Police did not immediately provide a statement on Thunberg when contacted by Reuters, but posted on messaging platform X that they had made 20 arrests in connection with protesters outside the hotel.

Speaking earlier at the protest, Thunberg had said, “The world is drowning in fossil fuels. People all over the world are suffering and dying from the consequences of the climate crisis caused by these industries.”

Environmental group Greenpeace said hundreds of demonstrators were involved in the protest, preventing delegates from entering the venue. It said two of its activists scaled the building and unfurled a giant banner over its entrance reading “Make Big Oil Pay”.

Inside the Intercontinental Hotel, two speakers, the chief executive officer of trading house Gunvor, Torbjorn Tornqvist, and the head of oil trading at Trafigura, Ben Luckock, missed the event after climate protesters blocked the entrance, a Reuters witness said.