(Adds details of intervention, fraud investigation)
BRASILIA, Oct 4 (Reuters) - Brazil's pension oversight body Previc ordered a 180-day intervention in Postalis Instituto de Previdência Complementar, the pension fund for post office workers, for breaking rules on reserve requirements and investments, the regulator said on Wednesday.
Postalis, Brazil's largest fund by number of participants, has amassed billions of reais in losses over the past decade due to risky bets and has run a deficit every year since 2011. Prosecutors in May charged eight people, including the fund's former president, with tax fraud and money laundering.
Previc took over management of Postalis for 180 days and ordered suspension of all the fund's executives and the freezing of their assets. A spokesman for the fund said the intervention "took us by surprise" and had no immediate comment.
Postalis oversees 10.2 billion reais ($3.25 billion) in savings for 155,400 contributing members.
Last year, a police investigation of fraud at Postalis and the pension funds of state-run banks Caixa Económica Federal, Banco do Brasil and oil company Petroleo Brasileiro SA uncovered alleged illegal operations and kickbacks paid to politicians in the midst of Brazil's biggest corruption scandal.
The funds controlled 280 billion reais in assets and have been an important source of investment in a credit-starved economy, but political connections at the funds raised questions about undue influence on their decisions.
Brazil's Federal Audit Court (TCU) separately found that fraudulent operations had caused 1 billion reais in losses at Postalis. In May, prosecutors charged eight people with defrauding the fund with overpriced investments between 2006 and 2011.
The head of the pensions industry trade group ABRAPP said the intervention in Postalis was an "exception" and no threat to Brazil's pension fund system that is solidly capitalized.
Last year, Reuters reported that the fund was trying to offload 2.2 billion reais worth of bad loans after a planned sale collapsed amid management changes and feeble demand.
Postalis extended loans to companies for years, a type of transaction that was increasingly used by state-controlled pension funds during the leftist Workers Partys 13 years in power. Some borrowers issued bank credit notes - known in Brazil as CCBs - that Postalis fully subscribed.
The pension fund's accounts turned red with the deterioration in corporate creditworthiness and capital markets activity in Latin Americas largest economy as it slowed down and slid into recession. ($1 3.1366 reais) (Reporting by Anthony Boadle; Editing by Susan Thomas, Andrea Ricci and David Gregorio)