By Agence France-Presse Thirteen people are in custody in France over the storming of the Paris offices of US investment giant BlackRock by activists who spray painted the walls and carpets with environmental and anarchist slogans, police said Tuesday. Around 100 climate and anticapitalist activists occupied the central Paris offices of the world's biggest private investment firm on Monday morning. "This intrusion was in no way peaceful. 17 arrests of which 13 are still in custody," the Paris police department tweeted, along with a video showing the destruction caused. The footage showed the walls and carpets covered in graffiti and documents strewn on the ground. "Our planet, your crime," read a slogan daubed on one wall in big black letters while in a corridor, the anarchist circle-A symbol had been sprayed on the carpet. In a statement, the Youth for Climate Paris group, which led the protest, accused the fund of investing in companies with environmentally destructive activities. But "in attacking BlackRock, we're attacking capitalism" as well, they said. Some of the graffiti referred to France's controversial pension reforms, in which some critics see the hidden hand of BlackRock. "Give back the pension," one slogan read. The intrusion was the second since the start of the year at BlackRock's Paris offices. Last month, dozens of striking rail workers briefly occupied the entrance, chanting slogans and lighting flares in a protest over the government's plan to fuse 42 pension schemes into one. Critics of the overhaul say it will force people to invest in private US-style pension plans -- to the benefit of foreign asset managers like BlackRock, whose French head Jean-Francois Cirelli recently received the Legion of Honour, France's highest distinction. BlackRock has denied trying to influence the reforms. It has also announced plans to clean up its investment portfolio by divesting from companies that get over 25 percent of their revenue from thermal coal production. But the firm, which was also targeted by climate protesters in London last year, continues to be viewed with suspicion among many on the French left. The leader of France's Greens, Julien Bayou, on Tuesday condemned the vandalism but maintained his fiercest criticism for the firm. "What I condemn is BlackRock, the biggest investor in fossil fuels, the biggest investor in the Amazon region," he said.