Moody's Investors Service had downgraded the senior debt and deposit ratings of 30 Spanish banks, citing heightened financial pressure on the country's sovereign rating and "many weak banks."

Of the lenders lowered today, 15 had their ratings cut by two levels and five by three or four levels, Moody's said in a statement.

The outlook on most banks' senior and deposit ratings remains negative, Moody's said.

Spain's credit rating was cut to Aa2 on March 10th by Moody's, which said the cost of shoring up the banking industry will eclipse government estimates.

The ratings company said then that Spanish lenders may need as much as €50 billion to meet new capital requirements, a figure that compares with the Bank of Spain's estimate that 12 lenders will need €15.2 billion.

"It seems increasingly plausible that hard choices will need to be made at some point over the rating horizon, balancing the sovereign's incentive to support the banks with the need to protect its own balance sheet," Moody's said.

"It is, in Moody's view, increasingly likely that the sovereign will not be prepared to write all banks a blank check."

Moody's said it maintained its Aa2 rating on the deposit and senior debt ratings of Banco Bilbao Vizcaya Argentaria SA, Banco Santander SA and La Caixa, all with a negative outlook.

Bloomberg