Hand grenades are becoming an increasingly popular way of issuing a gangland-related warning or blackmail and the number of incidents involving the explosives has shot up in the past two years.

Broadcaster RTL Nieuws reported on Tuesday that 23 incidents involving hand grenades were registered in the first four months of this year, compared with 42 in 2018 as a whole and just a handful of cases in the previous years.

In total, researchers from the University of Leiden have registered 117 cases in the past 11 years – one third of which took place in Amsterdam.

In most of the cases the grenade was left outside a cafe, club, shop or private home, or attached to the door handle. In 21 cases people were directly attacked or threatened with a grenade, resulting in nine people being injured, several seriously.

Judges in the Dutch capital said earlier this month that people convicted of crimes involving explosives would face tougher sentences.