The announcement came two weeks after night-time gunfire was reported outside Israel's embassy in Stockholm, and three months after police found a live grenade lying on the grounds of the Israeli compound.

"The Iranian regime is using criminal networks in Sweden to carry out acts of violence against other states, groups or people in Sweden that it considers a threat," the intelligence service, commonly known as Sapo, said in a statement.

It cited in particular "Israeli and Jewish interests, targets and operations in Sweden".

Tensions have flared between Israel and Iran since the start of the war in Gaza on October 7.

In a dramatic escalation after a years-long shadow war of killings and sabotage attacks between the arch-foes, Iran in April fired 350 drones and missiles at Israel, most of which were intercepted.

"Iran has previously used violence in other countries in Europe in a bid to silence critical voices and perceived threats against its regime," Sapo said.

"Our assessment is that this is a regional conflict that has spread globally and now also includes Sweden as an arena for this conflict," Sapo's counterintelligence chief Daniel Stenling told a press conference.

- Iran diplomat summoned -

Swedish Foreign Minister Tobias Billstrom said his ministry had summoned Iran's charge d'affaires for talks on Friday "to express how seriously we view this information".

"Sweden will not be a platform where state actors use criminal networks to promote their own interests," Billstrom said in remarks emailed to AFP.

The Scandinavian country has struggled to contain surging gang violence in recent years, with shootings and bombings now weekly occurrences across the country.

The gang violence was originally linked to control over the drugs market, but was "changing shape very quickly", the deputy head of the Swedish Police National Operations Division, Hampus Nygards, told the press conference.

The networks have increasingly recruited ever-younger youths and children eager to gain status and earn quick money, well aware they cannot be jailed if under the age of 15.

Stenling said Thursday that "very young individuals, even children, can be used to carry out Iranian activities that threaten security in Sweden".

- Foxtrot and Rumba -

Swedish newspaper Dagens Nyheter (DN) on Thursday cited documents from Israel's intelligence agency Mossad as saying that the head of the Swedish gang Foxtrot, Rawa Majid, and his arch-rival Ismail Abdo, head of the Rumba gang, had both been recruited by the Iranian regime.

DN said the Mossad documents showed that Majid -- a Swedish-Turkish dual national nicknamed the "Kurdish Fox" -- was recently arrested in Iran and ordered to cooperate with the Iranian regime or go to jail.

Swedish media meanwhile reported earlier this week that Abdo, who also holds Turkish citizenship, was recently arrested in Turkey during a traffic control and was released shortly afterwards on bail, despite an international arrest warrant.

Swedish Prime Minister Ulf Kristersson told media at the time that Abdo's release was "frustrating".

The Jerusalem Post also reported on Thursday, without citing any sources, that Mossad believed Iran was behind a grenade attack against Israel's embassy in Belgium last weekend.

Asked whether the Swedish intelligence agency's information about Iran came solely from Mossad, Swedish Justice Minister Gunnar Strommer told Thursday's press conference: "I feel very confident about the information our authorities have."

Sapo said it was collaborating with the police, military and international allies "to meet the threat from Iran".

Relations between Sweden and Iran have deteriorated since a Swedish court in July 2022 handed down a life sentence against a 63-year-old Iranian former prison official, Hamid Noury, for crimes committed during a 1988 purge of dissidents.

As Noury's trial got underway, Iran arrested Swedish EU diplomat Johan Floderus in April 2022, accusing him of spying for Israel which carries a potential death penalty.

Governments and human rights groups have accused Tehran of engaging in "hostage diplomacy".

No date has been set for the verdict in Floderus's case.