(Adds details on March 25 verdict with full decision published later)
FLORENCE May 14 (Reuters) - Italy's highest court has asked a lower tribunal to reassess whether investment bank Nomura committed fraud against Banca Monte dei Paschi di Siena through a large derivative contract, raising the spectre of a possible asset seizure.
The court dismissed, however, allegations that the Japanese bank had pocketed abnormal gains from the contract, known as "Alexandria", according to a transcript of the reasoning of the ruling reviewed by Reuters.
The court ruled on the case on March 25. But, according to Italian law, the full text of the ruling with the explanation behind the court's decision is only made available several weeks later.
Monte dei Paschi, Italy's third-biggest bank by branch number, was on the verge of collapse in 2012 after being hit by the euro zone crisis and risky derivative deals. The largest of these structured trades, Alexandria, is still in place.
Italian prosecutors investigating the derivative contracts at Monte dei Paschi ordered in April 2013 the seizure of 1.8 billion euros of Nomura's assets, a move aimed at preventing Monte dei Paschi from putting up more cash with Nomura to meet the collateral requirements of the Alexandria trade.
Later that month, a judge blocked the prosecutors' request saying there was no evidence the Japanese broker had made wrongful or disproportionate gains from the structured trades. An appeals court upheld that ruling on July 13.
Prosecutors lodged a final appeal with Italy's Cassation Court, the country's highest tribunal.
In its ruling, the Cassation Court asked a Siena-based court to reassess whether the content of a so-called "mandate agreement" linking the Alexandria notes to a further derivative contract on 30-year Italian government bonds had been clearly communicated to Monte dei Paschi.
Any potential seizure of Nomura assets would be significantly smaller than the initial request for 1.8 billion euros because the Cassation Court has decided to dismiss the allegation of usury, a legal source with direct knowledge of the case said.
Nomura has repeatedly denied any suggestion of wrongdoing. It and Monte dei Paschi declined to comment on Wednesday.
Monte dei Paschi is seeking 700 million euros in compensation from Nomura and two of its former bank executives.
The Tuscan bank dropped a parallel request for compensation from Deutsche Bank after reaching a deal in December to close a loss-making derivative contract known as "Santorini". (Reporting by Silvia Ognibene; Additional reporting by Lisa Jucca, editing by David Evans)