Sweden’s national bomb squad has been called out to 30 blasts in the past two months and 100 so far this year, more than twice the number in the same period in 2018, as concern grows about rising levels of violence by criminal gangs.

Police arrested three people over the weekend following an explosion in an apartment block in the southern city of Malmö early on Friday that blew out the building’s main door, shattered windows and substantially damaged the entrance level.

The blast was the first of three in the space of 24 hours, local media reported, with others destroying cars and damaging property in Växjö, 127 miles (204km) north-east of Malmö, and Landvetter outside Gothenburg on the country’s west coast.

“There are 10 million people in Sweden and I have not found the equivalent of this level of explosions in any industrialised country,” Ylva Ehrlin, an analyst with the bomb squad, told the public broadcaster SVT.

The number of recent explosions was “unacceptably high” and “obviously undesirable”, she told the news agency TT. “It’s very serious, a social problem. We not only must find the explosives and tools, but uncover the cause.”

Malmö’s police chief, Stefan Sintius, said there had been 28 explosions so far this year in Sweden’s third biggest city, scene of a string of gun and bomb attacks that right wing politicians have linked to the large flows of immigrants who arrived in in Sweden during the 2015 migration crisis.

Nineteen bombs have also exploded in the capital, Stockholm, so far this year, and another 13 in Gothenburg, compared with 39 nationwide in 2018. The squad have also defused 76 suspected bombs that were spotted before they could be detonated.

Ehrin said that although no one had died in the recent spate of explosions, the risk of fatalities must be considered very high. “We’ve been incredibly lucky. You just don’t usually have that kind of luck,” she said.

The bombs, which mostly target empty buildings, offices and cars, are usually small and experts believe they are intended to intimidate rival gangs. Police have said, however, that some could have been deadly. One device in Linköping earlier this year contained about 40 times the usual explosive charge, seriously damaging two residential buildings and injuring 25 people.

The bomb-makers themselves “usually do not know how dangerous, how sensitive these substances are” and are risking their lives, Ehrin said, noting that an 18-year-old man who was seriously injured when a bomb exploded in Malmö last December was later charged with trying to detonate it.

But the greater danger was to innocent bystanders, such as the female student who suffered severe facial injuries in September when a device inside a shop exploded as she was walking past on her way home from a night in Lund. “With a gun, you control it until you press the trigger,” Ehren said.

“Also, you usually aim at the intended target, but you do not have the same control over an explosive charge, especially if you are a criminal without much education or experience in the field. You have no control over the target or the effect.”

Experts have said the growing use of mainly plastic explosives is part of a wider increase in reckless violence among Sweden’s gangs. Fatal shootings ascribed by police to criminal networks have surged from an annual average of about four 20 years ago to more than 40 in 2018, official figures show.

The government has announced a 34-point plan to combat the violence, including measures making it easier for police to search homes and read encrypted phone messages. Denmark, however, is alarmed enough to have reintroduced border controls following two blasts in Copenhagen linked to Swedish gangs.

Despite the gang attacks, Sweden’s murder rate has fallen since the 1990s and remains among the world’s lowest, with killings linked to domestic violence, hate crime and “spontaneous fights” all significantly down.

• This article was amended on 7 November 2019 to state the actual number of bomb explosions in Malmö, rather than these being expressed as a proportion of the country’s total as in an earlier version.