Synagogues in Sweden have been shut down as a temporary precautionary measure after the country raised its terror threat level to ‘’high’’.

Police announced that they arrested Thursday night Moder Mothama Magid, a 22-year-old Iraqi man who has fought in Syria and who is accused of planning to launch a terror attack on the Swedish capital Stockholm.

Sweden, along with Denmark, on Wednesday raised its national terror threat status to "high", the second-highest level on a five-point scale, following an assessment by the National Center for Terrorist Threat Assessment (NCT).

Mats Sandberg, director of Sweden’s National Center for Terrorist Threat Assessment (NCT), told the media that the Islamic State terror group - which has claimed the Paris attacks - "considers Sweden a legitimate target".

Swedish Prime Minister Stefan Löfven admitted his country has been “naive” about the possibility of an Islamic State (ISIS) terror attack, adding Sweden would be stepping up security measures. h

According to the Swedish integration police chief, Ulf Boström, the city of Gothenburg, in western Sweden is, per capita, the European city from which most people have joined Islamic extremist groups.

Previous statistics from the Swedish security service, Säpo, suggest that just over 300 Swedish nationals have left the country to travel to fight with Islamic terorist groups in Syria and Iraq.

40 percent of those – around 120 young men – are from the Gothenburg area. According to Boström this means that Gothenburg is the European city which, in proportion to its population, contributes the highest number of people to violent extremism.