A band of 100 masked people staged a violent environmental protest in a quiet Moscow suburb, hurling Molotov cocktails and fireworks at city hall while objecting to plans for clearing a local forest for highway construction, Russian police said.

The centuries—old oak forest in Khimki has been a focus of controversy for years, as authorities plan to cut down much of the woods to make way for a major highway along the increasingly jammed route from Moscow to Sheremetyevo International Airport. In 2008, a local journalist who reported on the issue was brutally beaten and left crippled and brain—damaged.

Late Wednesday about 90 unidentified people attacked Khimki city hall, Moscow regional police said.

Russian television broadcast amateur video footage showing masked attackers throwing fireworks and bottles at the building, on which they had spray—painted “Save Russian forests” and “No to Khimki forest clearing.” Khimki officials said the attackers also threw Molotov cocktails.

City hall security officers stayed inside the building, and called police after the assailants had left, Khimki police chief Viktor Tanasiychuk said.

“Naturally, police squads did not find anyone at the scene when they arrived,” he said. Police said the attackers then left on a suburban train to Moscow.

No one was arrested at the scene, but police later detained nine environmentalists who have lived in the forest to stop loggers from clearing the trees. The activists denied any involvement in Wednesday’s attack, and a police spokesman confirmed they were not suspected in the attack. The spokesman said the activists instead are suspected of disturbing public order and resisting police, but he did not elaborate.

The head of the country’s Union of Environmental Non—Governmental Organizations, Andrey Morgulyov, accused police of detaining the activists to derail their plans to meet on Thursday with the Russian deputy natural resources minister and to attend a session on Friday of the Public Chamber on the Khimki forest.

Environmental protesters have become increasingly vocal in Russia in the recent years.

Thousands of people took to Moscow’s streets after Prime Minister Vladimir Putin signed an order this year to reopen a paper mill on Lake Baikal, the world’s oldest and deepest lake now believed to be under serious threat from industrial pollution and development. The lake holds an estimated 1,500 unique species of plants and animals.

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