The head of Greece's key privatization agency has resigned, citing lack of support from the new coalition government and warning that delays have left the privatization program well off-target.

In a blunt letter made public Friday, Costas Mitropoulos says revenues from the sale of state assets this year are unlikely to exceed €300 million ($366 million) — compared with a €3 billion ($3.6 billion) target.

The resignation is a deep embarrassment to the month-old, conservative-led government, which has described privatizations as its highest priority.

Mitropoulos wrote to the heads of the three governing coalition partners that their administration not only failed to support his agency, but also "indirectly but systematically" diminished its credibility in the eyes of potential investors.

Privatizations are a key part of Greece's commitments to bailout creditors.