ATHENS (Reuters) - Greece's banks met their bad loan reduction targets in the third quarter, bringing their so-called non-performing exposures down to 106 billion euros and attaining a targeted ratio of 51 percent, the central bank said on Wednesday.

Banks, which entered the crisis in 2008 with non-performing exposures (NPEs) of 14.5 billion euros or 5.5 percent of their loan books, saw them rise to 106.9 billion or 50.5 percent at end June this year.

The Bank of Greece, in cooperation with European Central Bank's banking supervision, will continue to monitor the implementation of banks' NPE action plans and may request additional corrective measures if deemed necessary, it said.

The mountain of NPEs, which include non-performing loans (NPLs) plus restructured loans likely to turn bad, is the biggest challenge facing the Greek banking system. Its reduction will free up capital to fund productive sectors of the economy.

"The resolution of private debt is of utmost significance for the rebalancing of the Greek economy towards export-oriented sectors and the efficient allocation of resources," the Bank of Greece said in a report.

Banks have agreed with regulators on ambitious bad debt reduction targets spanning a 3-year time horizon.

Greece's four systemic banks - Piraeus <BOPr.AT>, National <NBGr.AT>, Eurobank <EURBr.AT> and Alpha <ACBr.AT> - and three other less systemic bank have to submit data on nine operational targets, including on NPE and NPL gross volumes, cash recoveries via collections, liquidations or NPE loan sales.

Based on NPE operational targets submitted by the banks in September, their aim is to cut the NPE gross volume to 66. 7 billion by 2019 from 106.9 billion euros in September this year, meaning the NPE ratio to fall to 34 percent from 51 percent.

Likewise, their aim is to reduce their NPL ratio to 20 percent by 2019 from 37 percent in September.

"The reduction is mainly driven by curing of loans and write-offs and to a lesser extent by liquidations, collections and sales of loans," the report said.

(Reporting by George Georgiopoulos; Editing by Robin Pomeroy)