Dutch prosecutors say they have arrested a 48-year man on suspicion of preparing a terror attack, and a pistol and ammunition were found at his home in the northern city of Groningen.

The National Prosecutor's Office announced the arrest Wednesday and said an investigating judge has ordered the man detained for 90 days while investigations continue.

In a statement, prosecutors say the man, whose identity was not released, was arrested after a Dutch intelligence agency alerted authorities that he was a supporter of the Islamic State group and that he owned a weapon.

Police found the gun, hidden in a child's backpack, when they searched his home.

A day earlier, the Dutch counterterror coordinator maintained the country's alert level at four on a scale that tops out at five.