The EU faces a shortfall of some 2.5 billion euros to complete de-commissioning of eight ex-Soviet nuclear plants in Bulgaria, Lithuania and Slovakia, the European Court of Auditors said Wednesday.

In a damning report, assessing 2.85 billion euros of European Union monies already spent on the clean-up agreed with the three states during negotiations to join the EU, the Luxembourg-based court warned that "major infrastructure projects face delays and cost-overruns."

Covering work done between 1999 and 2010, it said authorities were still in the process of identifying tasks needing completion and warned that costings were incomplete "in the absence of key information on radioactive waste."

The court's inspectors said EU authorities still did not know how safe the sites would be, the report stating that "the degree of mitigation achieved is not known."

The court told the European Commission, the EU executive, to draw up a new schedule of works.

It also suggested that funding after 2013, when the EU enters a new, tighter-than-ever budgetary cycle, should rely more on existing grants allocated on the bases of national wealth, population or land mass, as opposed to one-off finance.