By Krisztina Than and Stephanie Nebehay BUDAPEST/GENEVA (Reuters) - Hungary's prime minister angrily accused illegal migrants on Friday of "rebelling" against the rule of law in his country as security forces across Europe struggled to control record flows of hungry, scared refugees. The United Nations called for the swift creation of large-scale reception centres in frontline states such as Hungary and Greece, and one U.N. agency warned that millions more refugees could arrive in Europe if Syria's civil war continues to rage. Many of the tens of thousands of refugees now trekking from Greece via the Balkans and Hungary towards western Europe are fleeing the Syrian war in search of sanctuary, above all in more welcoming and generous countries such as Germany and Sweden.