According to the police, the teenagers were non-fatally shot within minutes from each other on High Street, Wealdstone, on Sunday at around 13:17 GMT.
A spokesperson for the Metropolitan Police said that a 15-year-old teen and a 12-year-old boy suffering from gun wounds were treated by an ambulance at the scene before being transported to a hospital for further medical treatment.
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Their injuries are still being assessed and the police are waiting for details as well as an update on the boys' condition, according to the representative.
Nobody has been arrested so far and an investigation is underway.
The incident comes amid a major surge in violence in the British capital. The latest crime statistics for London reveal that since April 2017, the number of people murdered in Britain's capital has risen by 44 percent.
On April 9, the British government published a new crime prevention strategy, which aims to tackle the rise in violent crimes. The document, in particular, blames illicit drug markets for the high crime rate in the UK.
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In April, Louise Haigh, the shadow policing minister of the UK Labour Party, accused the Conservative Party of a failure to protect the public, since it shrank the nation's police force by 21,000 in comparison to 2010.