Sweden third largest city, Malmö, has built a reputation as the country’s Chicago. But it’s not just gun violence that’s blighted the port city. It’s borne the brunt of the hand-grenade attacks that have been on the rise in Sweden in the last couple of years: the number of grenade attacks jumped from eight in 2014 to 52 in 2016.

In most of them nobody was hurt, but an eight-year-old British boy, Yuusuf Warsame, was killed after a grenade was thrown into a flat in Gothenburg. He was the only death from a grenade attack since 2014, according to the Swedish Police Authority. There have been two injuries in that time period. Prime minister Stefan Löfven dubbed the summer of 2015 “the summer of unrest.”

Many of the grenades have been smuggled in from the Balkans, explains Manne Gerell, a criminology researcher at Malmö University who has been studying the attacks. “They are surplus weapons from the civil war,” he says, but “it’s not as well established exactly how they’ve come in [to Sweden].” In some cases, buyers of other smuggled weapons are given the grenades cheaply or for free as a bonus.

Last December, the government proposed tougher penalties (link in Swedish), which should take effect this July. The possession of explosives, such as grenades, would be penalized on the same scale as carrying firearms. The government proposed raising the minimum prison term from 6 months to a year, and imposing a new penalty scale of 3-6 years for the most serious cases. “Those who go out with a weapon should know that it could be several years before they are allowed to see their family outside of a prison again,” Löfven told parliament earlier this month.

Though the attacks appear random, authorities believe many to be linked with organized crime. “In most cases, either the suspect or the victim is associated with a criminal network,” Gerell says. He suggests the hand grenades are mainly used for intimidation, since many have been thrown into empty cars and buildings. The attack that killed Warsame was linked to an underworld feud.

These grenade attacks have occurred alongside a record influx of asylum seekers, which the main anti-immigrant party, Sweden Democrats, have been quick to capitalize on. ”It’s always people from other countries that do these things,” Jorgen Grubb, the party’s chairman in Malmö told Reuters. “What Malmö needs is to put up a red stop sign.”

Previously dubbed Europe’s most refugee-friendly country, Sweden has experienced rising unease over immigration. This has benefited the Sweden Democrats, once a fringe political group, who are now hoping to win a quarter of the votes in the 2018 general election (polls currently put them at 17%).

While some immigrants have been behind hand-grenade attacks, Gerell dismisses the argument that immigrants are driving a crime wave. “It’s a bit more complicated than that,” he says, adding that though there was a record influx of immigrants, “In Malmö, crime overall has actually been falling in the past five years.”