British police said Thursday they have arrested four people after protesters painted a giant Ukrainian flag on the road outside the Russian Embassy in London.

The campaign group Led By Donkeys said they painted the 5,400-square-foot blue and yellow flag to mark one year since Russia invaded Ukraine. It said activists wanted to remind Russian President Vladimir Putin that “Ukraine is an independent state and a people with every right to self-determination.”

The group said activists safely halted cars before pouring 35 gallons of paint on the road. Vehicles then spread the paint in both directions to create the flag, it said.

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London’s Metropolitan Police said officers arrested three men and a woman on suspicion of criminal damage and obstructing the highway. They remained in custody.