A 15-year-old boy in Britain has admitted involvement in a terrorism plot to attack police at this year's Anzac Day parade in Melbourne.

The teenager pleaded guilty at the Old Bailey to one count of inciting another person to carry out an attack at the event.

He entered his plea via video link from Manchester Crown Court.

The boy, who was 14 at the time, was arrested in April after police intercepted encrypted conversations allegedly with an 18-year-old man in Australia.

The prosecution dropped a second charge of inciting terrorism overseas in relation to beheading a person in Australia.

The boy, from the town of Blackburn in north-west England, cannot be named for legal reasons.

He is the youngest British person to be charged with terrorism offences.

Judge John Saunders said he had ordered pre-sentence reports because he wanted to find out if there had been any "indoctrination" of the defendant.

"Dealing with someone of this age is an extremely difficult sentencing process and I will need all the help I can get," the judge told the court.

The boy's arrest came as Australian police arrested five men in counter-terrorism raids in Melbourne on April 18.

Police at the time said it was believed the attacks were to have involved the use of "edged knives".

The 15-year-old is due to be sentenced in September.