COPENHAGEN, Denmark â€"  Denmark's security service says it has arrested two brothers of Somali origin suspected of plotting a terror attack.

The Danish Security and Intelligence Service, or PET, says the two men, ages 18 and 23, were arrested late Monday. One of them was arrested in the western city of Aarhus and the other as he arrived by plane at Copenhagen's international airport.

The agency says the arrests "have prevented a concrete act of terror" but didn't give any details.