A 30-second silence will be held at the start of the London Marathon on Sunday and runners are encouraged to wear a black ribbon to show support for Boston, organisers said on Tuesday.

The silent tribute will be held at the start of the elite men's race and mass start.

Race director Hugh Brasher said that ribbons will be given to all runners when they pick up their race number.

He said, "We want to show our support for our friends and colleagues in Boston at this difficult time for the global running community.

"We are determined to deliver an amazing event that will focus on one of the core pillars of the London Marathon, which is to have fun and provide some happiness and a sense of achievement in a troubled world'."

London police also promised that Sunday's race will be safe. Met Police Commissioner Bernard Hogan-Howe told the BBC: "We are reviewing our plans which is sensible ... We will increase searching, we will make sure we've got more officers on the street looking after people, making sure they're safe."

He added: "We've no reason to think they're any less safe than they were before the terrible events in Boston yesterday."

The London Marathon takes place with about 36,000 people participating.