Switzerland said Wednesday it had widened its probe into Malaysia's scandal-tainted state investment fund, 1MDB, with transactions worth $800 million under scrutiny and evidence pointing to fraud through "a Ponzi scheme".

The Swiss attorney general opened an investigation into the troubled 1Malaysia Development Berhad (1MDB) in August 2015 following allegations that some of the money allegedly stolen from the fund had passed through Swiss banks. 

Citing new evidence, the attorney general's office said in a statement it had "identified further suspect transactions involving the Swiss financial sector".

"The sum of USD 800 million (712 million euros) appears to have been misappropriated," the statement further said.  

It added that investigations showed 1MDB assets had passed through a Malaysian company called SRC in fraudulent transactions "based on a form of 'Ponzi' scheme".

Four individuals and one bank are currently targeted in the Swiss 1MDB probe. 

Attorney general Michael Lauber has asked Malaysia for further cooperation, his office said. 

Malaysian Prime Minister Najib Razak has faced fierce criticism over the 1MDB scandal, which now includes investigations in multiple countries, including the United States. 

A Najib spokesman did not immediately respond to a request for comment.

The Malaysian prime minister is clinging to power despite increasingly damaging allegations that he took part in the alleged looting of billions in state funds.