LONDON (AP) — Police officers from across Britain are lining the streets of London for a funeral procession for the policeman killed in an extremist attack last month.

Constable Keith Palmer was stabbed to death by Khalid Masood on March 22 as he guarded the cobbled forecourt of the Palace of Westminster.

Police said Monday the scale of the funeral will be unprecedented, with two minutes of silence to be observed by police throughout the country.

Sara Thornton, head of the National Police Chiefs' Council, says "we all want to pay honor to the ultimate sacrifice that Keith made."

Palmer's coffin lay overnight in a chapel at Parliament after special permission was granted by Queen Elizabeth II.

Masood killed four other victims as he rammed pedestrians on Westminster Bridge with a rented SUV.