Nomura, which signalled its intention to become a global investment banking powerhouse with the acquisition of Lehman Brothers' European operations last year, has been dealt a blow after ratings agency Moody's Investors Service downgraded the bank's debt ratings on concerns over its ability to successfully integrate the US bank's operations.

Moody's said in a statement today that it had downgraded Nomura Securities' senior unsecured debt rating from A2 to Baa1, while its short term debt rating was also cut from Prime-1 to Prime 2. Nomura Holdings, the parent holding company, has also been downgraded to Baa2 from A3.