Swedish police on Thursday arrested four people suspected of links to “violent Islamist extremism” who were plotting a terrorist attack, the security service and the Sapo criminal investigation agency said, Reuters and AFP reported.

“They are suspected of preparing terrorist acts and committing serious crimes with the use of weapons,” the SBU reported.

“The case is about violent Islamist extremism,” Sapo continued, adding that there were also links to organized crime.

In a statement, the prosecutor’s office confirmed the fact of the arrests and said that the investigation is being conducted by a prosecutor from its security department, but did not provide details.

No further details about the alleged links to IS, the identities of the suspects or the nature of the alleged planned attack were provided.

The arrests came after a thorough investigation into the case, the police said in a statement. The National Prosecutor’s Office said separately that the arrests were made in the Stockholm area.

Expressen newspaper reported that residents heard several loud bangs as police stormed buildings in the southern suburbs of Stockholm.

Swedish media reported that a large number of police, led by the security service, made arrests in Tireso.