Dutch police who arrested a French national in Rotterdam on suspicion of "planning a terror attack" found ammunition at a house they searched.

Wim de Bruin, a spokesman for the national prosecutor's office, said Monday that police who carried out raids the previous evening seized items including ammunition, money and drugs. He declined to elaborate on the sort of ammunition.

A special police unit arrested the 32-year-old Frenchman at the request of French authorities who suspect him of "involvement in planning a terror attack," prosecutors said. He is expected to be swiftly extradited to France.

De Bruin says three other men, all with Algerian backgrounds, also were detained during the operation, but are not wanted by France.