Swiss supervisor FINMA accused BSI, a merchant bank, of "serious breaches" of money-laundering regulations in its dealings with the Malaysian sovereign wealth fund 1MDB, which is at the heart of the corruption allegations.
In the toughest punitive action yet announced in the affair, FINMA said in a statement it was approving the takeover of the merchant bank by Zurich-based private banking group EFG International on the condition that BSI is integrated "and thereafter dissolved" within 12 months.
FINMA said it was investigating two former top managers, who were not identified, to determine what they knew about the illegal activities, warning that it may launch further probes.
"In the case of 1MDB, the bank executed numerous large transactions with unclear purpose over a period of several years and, despite clearly suspicious indications, did not clarify the background to these transactions," the Swiss regulator said.
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The fund, which ran up more than USD 11 billion in debt in a series of much-questioned investments, has steadfastly denied money was stolen or that it was in financial trouble.
Najib also faced questions after the Wall Street Journal revealed USD 681 million in transfers to his personal bank accounts.
But since the scandal erupted last year, Najib has weathered the allegations by curbing scrutiny by authorities, purging officials demanding accountability, and stifling media reporting.
In a more recent report, the newspaper said Malaysian investigation documents indicated more than USD 1 billion in 1MDB-linked money had been funnelled to Najib.
Najib and 1MDB vehemently deny that claim.
Najib has faced calls to resign but has tightened his grip on the ruling party and thwarted domestic investigations. His position is not seen as being under imminent threat.