LONDON (AFP) - A woman was found beheaded on Thursday in a back garden in north London, according to media reports, but police said the attack was not linked to terrorism.

Police discovered the body of Palmira Silva, 82, in the suburb of Edmonton after being alerted at midday by local residents who said a man with a knife was attacking a cat or dog.

They would not confirm reports she had been beheaded, nor some media descriptions that the act was carried out with a machete.

A 25-year-old man has been arrested on suspicion of murder and is in custody, they said. Police evacuated residents from their homes as the man ran through a row of back gardens.

"At first there were two police cars, then all of a sudden there were 20," one witness, 19-year-old Ahmed Yusuf, said.

"The police said to drop everything ... They said there's a guy jumping over gardens."

Scotland Yard said it was also investigating an attempted attack on two people at another house in the same road shortly before the attack on Silva.

"At this stage we believe they were both able to get out of the house without injury," said a police spokesman.

Detective Chief Inspector John Sandlin of Scotland Yard said they were not looking for anyone else over the incident.

"This was a highly visible attack in broad daylight on a residential street," he added.

"Whilst it is too early to speculate on what the motive behind this attack was, I am confident based on the information currently available to me that it is not terrorist-related.