Four people have been arrested after campaign group Led By Donkeys painted a Ukrainian flag on the road outside the Russian Embassy in London.

The group claimed responsibility for the 500 square metre blue and yellow flag, painted on Bayswater Road in London on Thursday, saying they did it to mark Friday's first anniversary of Russia's invasion of Ukraine.

"Tomorrow is the first anniversary of Putin's imperialist invasion of Ukraine," the group said in a statement.

"Contrary to what the Russian dictator and his apologists claim, Ukraine is an independent state and a people with every right to self-determination.

"The existence of a massive Ukrainian flag outside his embassy in London will serve to remind him of that."

The flag is the latest stunt from the activists, famed for their giant billboards of politicians' tweets.

The Metropolitan Police said three males and one female had been arrested on suspicion of criminal damage and obstructing the highway.

"At 08:45 today officers attended Kensington Palace Gardens, where paint had been thrown on the highway," the Met said in a tweet.

"Four people, three males and one female, were arrested on suspicion of criminal damage and obstructing the highway.

"They remain in custody."

The campaign group said they created the flag by spreading 170 litres of yellow paint on the eastbound carriageway and a similar amount of blue paint on the westbound side.

Passing traffic then spread the paint along the road.

The activists added that the paint was "high-standard, non-toxic, solvent-free, eco-friendly, fast-dry edible paint designed for making road art".