Gang wars have brought an "unprecedented" wave of violence to Sweden, the national police chief said Wednesday, following a series of fatal shootings in the space of a week.

For years now, Sweden has been in the grip of a war between gangs fighting over arms and drug trafficking, involving firearms and explosive devices.

"There have recently been murders and explosions on an unprecedented scale," police chief Anders Thornberg told a press conference.

"Several boys aged between 13 and 15 have been killed, the mother of a criminal was executed at home, and a young man in Uppsala was shot dead on his way to work", he added.

The police chief emphasised that the perpetrators were often from abroad, without mentioning any nationalities.

There have been several shootings in Sweden this week: four in the university city of Uppsala -- two of them fatal -- and two in Stockholm, where a 13-year-old teenager lost his life.

Last year, 90 explosions and 101 attempted explosive attacks were recorded, according to data from the Swedish police.

So far this year over 100 explosions have already been recorded.

The conflicts between these criminal gangs are costing innocent lives, said Thornberg.

"Citizens are afraid, insecurity is increasing. And this at a time when we have raised our terrorist alert level in the country".

Several gang crimes have been foiled in recent days, he added, stressing the importance of preventive work.

"Several people have been arrested and weapons confiscated in Uppsala alone, where the situation is very serious", added Ulf Johansson, a police officer in the Uppsala region, which is 70 kilometres north of Stockholm.

In 2022, there were 391 shootings in Sweden, 62 of which were fatal, compared to 45 people killed by gunfire the previous year.