Three Swedish centre-right parties have announced they have reached a deal to form a coalition government that would not include the anti-immigration Sweden Democrats, but would depend on their support in parliament.

The agreement comes after a month of talks following September 11 elections that gave the Sweden Democrats, a party with right-wing extremist roots, an unprecedented position of influence in Swedish politics.

Opposition leader Ulf Kristersson said that his conservative Moderate party would form a centre-right coalition government with the Liberals and the Christian Democrats.

The Sweden Democrats would be outside the coalition but would help shape government policy from the sidelines.

The centre-right coalition depends on the support of the Sweden Democrats to secure a majority in parliament.

The party, founded by neo-Nazis and other far-right activists, has moved toward the mainstream under Jimmie Akesson, who since taking over the party in 2005 has elevated it from fringe movement to become Sweden’s second biggest party, with more than 20% of the vote.

Mr Akesson said he would have preferred cabinet seats for his party but he supported the deal that would give the Sweden Democrats influence over government policy, including on immigration and criminal justice.

“For us, it has been absolutely decisive that a shift in power must be a paradigm shift when it comes to immigration policy,” Mr Akesson said, adding that Sweden’s rules on asylum should be no more generous than required by the European Union, of which Sweden has been a member since 1995.

Sweden along with Germany stood out in Europe for its generous welcome toward asylum-seekers from the Middle East and Africa until the migration crisis of 2015-2016 prompted stricter controls.

A rise in gang violence in neighbourhoods dominated by immigrants has led to widespread calls for even tighter controls on immigration and tougher sentences and deportations for foreign citizens who commit crimes in Sweden, policies long espoused by the Sweden Democrats but emulated in recent years by parties both on the centre-left and centre-right.

Mr Kristersson, who is expected to lead the next government, said his coalition and the Sweden Democrats had agreed to increase prison sentences for gang members, including those under 18, and introduce special visitation zones for police to crack down on crime.

“We will also carry out a thorough review of the entire penal code, with tougher penalties for violent and sexual crimes,” Mr Kristersson said on Facebook.

Mr Kristersson will meet the speaker of parliament, who is expected to task him with forming a cabinet. A parliamentary vote on electing Mr Kristersson as prime minister is expected on Monday.

Prime Minister Magdalena Andersson of the centre-left Social Democrats continues to lead in a caretaker government capacity until a new government is formed.