An Italian judge has rejected an order to seize around 1.8 billion euros ($2.3 billion) of assets from Nomura <8604.T> as part of a probe into suspected fraud involving troubled lender Monte dei Paschi di Siena , a judicial and a legal source said on Saturday.

Prosecutors in Siena are investigating risky derivatives trades that have endangered the survival of Monte Paschi, the world's oldest bank.

They ordered the seizure of around 1.8 billion euros of assets from the Japanese bank on April 16, but the court has rejected their request to have it validated.

A spokeswoman for Nomura in Italy had no immediate comment.

(Reporting by Silvia Ognibene, writing by Gavin Jones, editing by Danilo Masoni)