New York City police commissioner William Bratton has said the majority of the city's drug-related violence is related to marijuana, as he blasted states that have legalized the substance.

'Here in New York, the violence we see associated with drugs, the vast majority of it is around the issue of marijuana,' Bratton said on Sunday during an appearance on the Cats Round Table radio show.

'I have to scratch my head as we are seeing many states wanting to legalize marijuana, and more liberalizations of policies,' the top cop continued.

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William Bratton (pictured in November) holds up a bag of oregano to demonstrate what a bag of weed looks like. Bratton said that marijuana trafficking is behind the 'vast majority' of drug-related violence in the city

Bratton's comments came after a brief discussion on a spike in heroin use in the city, and the radio show host John Catsimatidis asked no follow-up questions.

The commissioner was referring specifically to violence 'associated with the sale of marijuana,' an NYPD spokesman clarified in an email to Daily Mail Online.

The police spokesman refused to say whether there are any statistics on drug trafficking-related violence.

In 2014, mayor Bill de Blasio loosened restrictions on cannabis possession in New York City.

Since November that year, New Yorkers found in possession of 25 grams of less of the drug are slapped with a fine rather than arrested.

Arrests for marijuana possession went down by 42 per cent in 2015 compared with the previous year, according to New York State Criminal Justice Services statistics.

De Blasio said he pushed for the policy change because low-level drug arrests disproportionately affect black and Latino communities.

Massive haul: In this February 2016 photo, the NYPD shows off some 300 pounds of cannabis seized in a raid in the West Village

But the mayor and the police commissioner appear to have differing views on the danger that marijuana poses to the city.

Bratton first made the connection between marijuana and violence in early 2015, just a few months after the change in marijuana policy went into effect.

'In this city, people are killing each other over marijuana... The seemingly innocent drug that's being legalized around the country,' Bratton said in March that year, according to the New York Times.