Estonia's banking system is 95 percent controlled by four Nordic financial groups, and concerns over the scale of bad debt in an economy that was badly hit by the financial crisis have weighed on shares in Swedbank and SEB among others.

"Companies, most of all real estate firms' loan portfolios, were added to those in payment difficulties," the bank said in a statement.

The size of Estonia's loan and leasing portfolio in April was 14.4 billion euros ($20.26 billion) down from 14.5 billion euro in March.

The Estonian central bank expects overdue loans to stabilise at 5.0 percent of the total loan portfolio by the end of 2011. Estonia joined the euro zone from Jan 1 2011.

Copyright Reuters, 2011