The Greek debt management agency said the yield had risen to 4.8 percent from 4.75 percent offered in the last six-month bill sale in March.

"Total bids reached 4.758 billion euros and the amount finally accepted was

1.625 billion," the agency said.

The auction had originally aimed to raise 1.25 billion euros.

The issue came as the Greek government is labouring to keep a draconian overhaul of the recession-hit economy on track, under pressure from the EU and the IMF which last year bailed out Athens with a 110-billion-euro loan.

The government had hoped progress on slashing the runaway Greek deficit would restore confidence in the economy and enable a return to borrowing markets with longer-term bonds later this year.

But the spread, or gap, between 10-year Greek bonds and German equivalents is still around 10 percentage points.

A series of damaging downgrades from the three main debt rating agencies,

Moody's, Standard & Poor's and Fitch, has further complicated matters, leading the finance ministry to now consider a 2012 market sortie.

Since the EU-IMF bailout Greece has only felt able to issue three-month and six-month treasury bills, with their relatively lower yields.

Since the bankruptcy rescue, Athens has been issuing treasury bills twice a month. It skipped a three-month auction in March because the money was not needed, the finance ministry has said.

Analysts say the government will eventually have to restructure the country's massive debt, which currently stands at around 340 billion euros.

Greek authorities have repeatedly ruled out the prospect.