Counter - terrorism operations in Europe have uncovered an ISIS sleeper cell in Denmark . Officials fear that it was planning an attack similar to the March suicide bombings in Brussels ( Belgium ) . Four suspects were arrested on 7 April in the capital , Copenhagen , and are believed to have been recruited by extremists operating in Syria . Danish authorities have been on high alert since two people were killed in shooting attacks on a free speech event and a synagogue in Copenhagen in February last year. During a related search in the city , ammunitions and weapons were found . The Danish authorities have been on high alert since two people were killed in attacks on a free speech event at a synagogue in the capital in February 2015 . It is believed that more than 125 people have left the country to join ISIS .
Counter - terrorism operations in Europe have uncovered an ISIS sleeper cell in Denmark . Officials fear that it was planning an attack similar to the March suicide bombings in Brussels ( Belgium ) . Four suspects were arrested on 7 April in the capital , Copenhagen , and are believed to have been recruited by extremists operating in Syria . During a related search in the city , ammunitions and weapons were found . The Danish authorities have been on high alert since two people were killed in attacks on a free speech event at a synagogue in the capital in February 2015 . It is believed that more than 125 people have left the country to join ISIS .