ROME, Jan 22 (Reuters) - Giuseppe Mussari resigned as head of Italy's banking lobby ABI on Tuesday after a source said Banca Monte dei Paschi di Siena, where he served as chairman until last year, would book a 220-million-euro loss on a three-year-old derivative contract.
"I made this decision convinced that I have always respected the rules of our association, but at the same time I did not want to harm in any way our association," Mussari said in his resignation letter, which was obtained by Reuters.
Mussari made no mention of the Siena bank or of the derivative contract.
Japanese bank Nomura, which designed the 2009 derivatives deal for Monte dei Paschi, said earlier on Tuesday the trade had been reviewed and approved by Mussari. (Reporting by Stefano Bernabei, writing by Steve Scherer)