Moody's Investor Service downgraded the senior debt and deposit ratings of 30 Spanish banks with negative outlook for most banks, adding pressures on Spain after cutting the country's credit rating.

Moody's downgraded 15 banks by two notches, five banks by three or four notches, while it kept the Aa2 rating for the three biggest banks, which are Banco Bilbao Vizcaya Argentaria SA, Banco Santander SA and La Caixa, unchanged.

The rating agency attributed the cut to the escalating concerns with regard Spain's sovereign debt, fragility of many banks, especial small and regional ones which lack support across the whole old continent.