Prosecutors investigating the affair of collapsed food group Parmalat asked a Milan judge on Friday to send four leading global banks to trial for their role in the dairy firm’s collapse, according to a judicial source quoted by the news agency Reuters.

The investigating magistrates also asked Judge Cesare Tacconi to order 13 bankers and an Italian asset management firm to stand trial for allegedly helping the food group mislead investors, the source said.

The foreign banks are Citigroup and Morgan Stanley of the United States, Germany’s Deutsche Bank and Swiss bank UBS. The fifth firm is asset manager Nextra, which Italy’s Banca Intesa is selling to France’s Credit Agricole.

The request for trial was the latest legal development in a scandal that has spawned several suits and counter-suits. The move had been expected and was considered a technical step after prosecutors named the accused in a probe they closed in March.

Hearings on the request are due to begin in September.

The banks have previously denied wrongdoing in Parmalat’s €14bn (US$17bn) collapse.

On Friday, Morgan Stanley, Deutsche Bank and Nextra declined to comment on the matter.

UBS said it had been made aware of the prosecutors’ step, and did not consider its behaviour or that of its employees to be linked to market manipulation.

Citigroup denied that the bank or its employees acted incorrectly.

The 13 executives, all from the five firms except for an employee of Credit Suisse First Boston, were accused by prosecutors of breaching Italian market-rigging laws.

CSFB declined to comment.