CARACAS (Reuters) - Venezuelan state elections may be repeated in the five states won by the opposition if the governors-elect continue to refuse to be sworn in by a controversial pro-government legislative superbody, President Nicolas Maduro warned on Friday. His warning came in a televised speech after the government on Sunday unexpectedly won 18 of 23 states in a vote which the opposition calls fraudulent. Authorities have mandated that all elected governors participate in a ceremony before the pro-government Constituent Assembly, but the five opposition winners did not take part.     Anyone who wants to be governor will have to recognize the Constituent National Assembly; otherwise elections will be repeated in states where the Assembly is not recognized,  Maduro said at the inauguration of one of the socialist candidates in western Lara state.     The opposition says that by law, the oath must be taken before regional parliaments and not before the Constituent Assembly, but so far none of their candidates have undergone that process and formally assumed their roles.     Venezuela s opposition leaders have said they would travel abroad to denounce what they call dirty tricks by the government and outright fraud in the minerals-rich state of Bolivar. Maduro says the opposition cries fraud whenever it loses elections and that Venezuela s electoral system is the most secure in the world. 