Swiss prosecutors are investigating whether the country's financial industry was used in the alleged misappropriation of $800 million from a former subsidiary of Malaysian state fund 1MDB.

Switzerland's Office of the Attorney General (OAG) said on Wednesday a Ponzi scheme may have been set up to conceal the alleged fraud, adding it was seeking further help from Malaysia for its investigation.

1Malaysia Development Berhad, commonly known as 1MDB, was founded by Malaysian Prime Minister Datuk Seri Najib Tun Razak in 2009 shortly after he came to office, and is currently being probed for money-laundering in several countries.

Both 1MDB and Najib have repeatedly denied any wrongdoing.

The OAG, which has been running an investigation around 1MDB for more than a year, said evidence allegedly now showed fresh "suspect transactions involving the Swiss financial sector".

"Firstly, the sum of $800 million appears to have been misappropriated from investments in natural resources made by the SRC sovereign fund," it said in a statement, referring to a former 1MDB subsidiary.

"Secondly, it is suspected that a 'Ponzi' scheme fraud (i.e. paying the returns on initial investments from funds obtained from subsequent investors rather than from legitimate revenue from the investments) was committed to conceal the misappropriations from both the SRC fund and from 1MDB."

At this stage of its criminal proceedings in connection with 1MDB and SRC International, four people and one bank are under investigation, the OAG said. It did not name the individuals or the bank on Wednesday.

The aim of the latest OAG request for Malaysian help is to gather further evidence to support these findings, the OAG said, adding an initial request for assistance in January was still pending.

1MDB and Malaysia's Attorney General's office did not immediately respond to requests for comment.

In May, the OAG said it had opened criminal proceedings against Lugano, Switzerland-based BSI bank as part of its investigations surrounding 1MDB. BSI is in the process of being bought by EFG International.

BSI did not directly comment on the proceedings at the time, but said group CEO Stefano Coduri had stepped down with immediate effect and it had undertaken steps to strengthen management, including introducing a new chief risk officer and appointing a new group legal counsel.

The OAG also said in April it had extended its criminal proceedings to two former Emirati officials, in charge of Abu Dhabi sovereign funds. It did not name the officials or funds.