RIO DE JANEIRO (Reuters) - Brazilian authorities were serving 127 arrest warrants in six states on Monday as part of a year-long investigation into international drug traffickers who have shipped at least six tonnes of cocaine to European cities, federal police said. Operating out of the Brazilian ports of Santos, Salvador and Itaja , the drug gangs sent the cocaine to Antwerp in Belgium, Gioia Tauro in Italy and Valencia in Spain, police said. The U.S. Drug Enforcement Administration (DEA) collaborated in the investigation, Brazilian police said in a statement. The warrants were being served in the states of S o Paulo, Minas Gerais, Santa Catarina, Paran , Rio Grande do Sul and the Federal District. 