A statement from the prosecutor's office in Siena said it had ordered the seizure of "a total of around €1.8 billion euros from Nomura International" including €88 million in commissions and 1.7 billion euros in collateral posted by Monte dei Paschi for Nomura.
Prosecutors also seized a total of €14.4 million from three former managers of Banca Monte dei Paschi di Siena who are under investigation.
It placed under investigation Sadeq Sayeed, the former head of Nomura for Europe, Middle East and Africa, as well as Raffaele Ricci, a managing director for fixed income sales.
Sayeed stepped down from Nomura in 2010.
The statement said Sayeed and Ricci were suspected of "gravely obstructing" the activities of supervisory authorities and putting out "false statements".
Contacted by AFP, Nomura declined to comment.
The world's oldest bank, Monte dei Paschi di Siena has been at the centre of a massive fraud scandal since January which has uncovered several derivative deals put in place by its former management in order to disguise losses.
The bank itself last month began a lawsuit in civil court against Nomura, Deutsche Bank and two of its former managers for their role in these operations.
Investors cheered the prosecutorial action, with Monte dei Paschi's shares jumping by more than 3.0 percent on the Milan stock exchange by 11:00 GMT, while the benchmark index was down 0.46 percent.