The head of London's police force says the number of hate crimes against Muslims in the city increased substantially after the killing of soldier Lee Rigby.

Bernard Hogan-Howe said in a web chat Wednesday the number of hate crimes reported to police went from one per day to eight per day after the May 22 slaying.

He says the number has since dropped to two per day.

Two Islamic extremists are accused of killing Rigby near his army barracks. One suspect was filmed boasting of the killing moments afterward in a widely broadcast video.

Hogan-Howe said extra police patrols have been added around "high-risk" sites.

There have been a number of arson attacks on mosques throughout Britain since the killing. Some mosques have been defaced with graffiti.