Sweden is home to 2,000 Islamist extremists, the nation's intelligence chief revealed today - ten times the number recorded before Europe's migrant crisis.

Anders Thornberg, head of domestic spy service Sapo, attributed the rise primarily to the sophisticated propaganda machine of ISIS.

Although 'few extremists' have 'the will and ability' to carry out attacks, they must be found and closely followed, Thornberg said.

Sweden is home to 2,000 Islamist extremists, the nation's intelligence chief revealed today - ten times the number recorded before Europe's migrant crisis. The country has been on edge since a jihadist moved down pedestrians in Stockholm in April, killing five

'It's important that everyone in Sweden takes responsibility to end this trend... before we see an attack or a violent act,' Thornberg told news agency TT in an interview published on Monday.

Sweden has been on the edge ever since an Uzbek national, who had shown sympathies for jihadist groups including ISIS, used a stolen truck to mow down pedestrians on a busy shopping street in Stockholm on April 7, killing five people and injuring 15.

Europe has seen a string of attacks in recent years including large-scale assaults in Paris Brussels and Berlin.

Thornberg said that out of around 3,000 violent extremists currently in Sweden, 2,000 have Islamist motives. The remaining extremists originate from far-right and extreme-left movements.

About 300 people from Sweden are known to have travelled to Syria and Iraq to join ISIS since 2012, officials have said (file picture)

A 2010 Sapo report estimated the number of violent Islamist extremists in the Scandinavian country at 200.

Sapo has previously said that about 300 people from Sweden are known to have travelled to Syria and Iraq to join ISIS since 2012.

Around 140 have returned to Sweden and about 50 are said to have died abroad.

Jihadists or sympathisers from Sweden have been linked to several terrorist attacks in recent years, as a Swedish national, Osama Krayem, has been charged with terrorist murders over the 2016 Brussels metro bombing.