BUCHAREST, Jan 22 (Reuters) - Romanian authorities have arrested three men suspected of stealing paintings by Picasso, Matisse and Monet from Rotterdam's Kunsthal museum in October, local news agency Mediafax said on Tuesday. Thieves made off with seven paintings, which also included a Gauguin, a Lucian Freud and a Meyer de Haan, thought to be worth tens of millions of dollars in a brazen and meticulously planned operation.