A man has been arrested after scaling a perimeter wall at Buckingham Palace, the residence of Britain's Queen Elizabeth, London police said.

Police said the man was detained in the palace's grounds on suspicion of trespassing on a protected site shortly after 8.30 p.m. yesterday, seven minutes after an alarm was activated.

Police said the man was not armed.

"I am content that our security measures worked effectively on this occasion and at no time was any individual at risk," said Commander Adrian Usher, head of London police's Royalty and Specialist Protection unit.

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