Sweden's prime minister summoned the head of the armed forces and the police commissioner in a bid to stem gang violence, following a wave of violence that has taken at least 11 lives in September alone.

Two people were killed in separate shootings in Stockholm on Wednesday, and a woman in her 20s, thought to be an innocent bystander, was killed when a bomb tore up a house in Uppsala.

"This is a difficult time for Sweden. A 25-year-old woman went to bed last night on a completely ordinary evening but never got to wake up," Prime Minister Ulf Kristersson said during a rare televised address to the nation.

"We will hunt the gangs, we will defeat the gangs," he said.

Kristersson formed a centre-right minority government after last year's election with support of the populist and anti-immigrant Sweden Democrats, ending eight years of Social Democrat-led governments in Sweden.

His coalition won the election partly on a promise to stem growing gang violence, and it has launched a series of initiatives, such as greater powers to police and harsher punishment for gun crimes.

The measures have yet to take effect, but Kristersson blamed former governments for the problems.

"It is an irresponsible immigration policy and a failed integration that has brought us here," Kristersson said.

Sweden had liberal immigration policies for many decades and took in more immigrants per capita than any other European nation during the 2015 migration crisis. Those policies were reversed by the former Social Democrat-led government, but have been tightened by Kristersson's government. About 20% of Sweden's 10.5 million inhabitants were born abroad.

Earlier on Thursday, the opposition Social Democrats, the biggest party in parliament, called on the government to change the law, allowing the military to help stop the gang violence.

"This is not Sweden, this is not how Sweden is supposed to be," Social Democrat leader Magdalena Andersson told a news conference.

Kristersson said he had summoned the national police commissioner and the supreme commander of the armed forces to evaluate the options.

The police estimate that about 30,000 people in Sweden are directly involved with or have ties to gang crime. The violence has also spread from major urban areas to smaller towns where violent crime was previously rare.

Earlier this week, two people were shot dead and two injured when a gunman opened fire at a bar in Sandviken. The 11 shooting deaths this month make September the deadliest month since December 2019.

"The criminal conflicts in Sweden are a serious threat to the safety and security of the country," National Police Commissioner Anders Thornberg said in a statement.

"Innocents are murdered and injured. We are doing everything we can within the police and together with others to stop the development."