Swiss prosecutors have asked Malaysian authorities for help investigating the possible disappearance of about $4bn from a state-owned company at the centre of a corruption scandal.
Investigators believe the funds - earmarked for economic and social development projects - may have been stolen.
"A small portion" of the cash was transferred into Swiss accounts held by former Malaysian officials as well as current and former officials from the United Arab Emirates, the Swiss attorney general's office said in a statement on Friday.
"To date, however, the Malaysian companies concerned have made no comment on the losses they are believed to have incurred," prosecutors added.
READ MORE: Support for Malaysia's PM Najib dwindles after scandal
"The object of the request for mutual assistance is therefore to advise the companies and the Malaysian government of the results of the Swiss criminal proceedings, with the aim of finding out whether losses on this scale have been sustained."
In September, authorities announced the freezing of "tens of millions of dollars" worth of assets held in Swiss accounts as part of the investigation.
The attorney general's office said the assistance request was made as part of criminal proceedings opened last August against two former officials of Malaysian state-owned fund 1MDB (1Malaysia Development Berhad) and "persons unknown".
They are suspected of bribing foreign officials, misconduct in a public office, money laundering and criminal mismanagement, the office said.
Derision and questions
"So far four cases involving allegations of criminal conduct and covering the period from 2009 to 2013 have come to light," the statement said, "each involving a systematic course of action carried out by means of complex financial structures."
The assistance request had already been discussed at a meeting between the Swiss attorney general and his Malaysian counterpart in Zurich in September, the statement added.
Malaysian Prime Minister Najib Razak has been under heavy political pressure over allegations that hundreds of millions of dollars were missing from deals involving 1MDB.
He has for months denied accusations that huge payments into his own bank accounts -- just before a hotly contested 2013 general election -- were syphoned from the now-struggling state-owned company.
The Malaysian attorney general's office said in a statement on Saturday it would take all possible steps to follow up and collaborate with its Swiss counterpart, but noted that the investigations into donations made to Najib were entirely separate from those into 1MDB
Najib was cleared of corruption on Tuesday when Malaysia's attorney general said the Saudi royal family was the source of the $681 million "donation" to his personal accounts. Najib returned $620m to the Saudis as the money was not used, attorney general Mohamed Apandi Ali said.
The announcement triggered derision and fresh questions in a country well-used to graft allegations.