Italian authorities have seized 1.8 billion euro ($2.35 billion) from Japan's Nomura bank and placed its former European CEO under investigation as part of its probe into the trading scandal at Monte Paschi di Siena bank.

Siena prosecutors said Tuesday Nomura's retired Europe chief, Sadeq Sayeed, and Raffaele Ricci, a managing director for fixed income sales, were accused of obstructing regulatory authorities. Nomura declined comment.

Monte Paschi, the world's oldest bank, has been embroiled in a derivatives scandal that has cost it some 730 million euros and forced it to request an increase in state aid to keep afloat.

The bank has said it would sue former chairman Giuseppe Mussari and former general manager Antonio Vigni, along with Nomura and Deutsche Bank, over the two costliest trades in the scandal.