The European bail-out fund should be doubled to 1.5 trillion euros ($2.15 trillion) if politicians want private sector investors to participate in a second bail-out package for Greece, a European Central Bank governing council member said.

Nervous markets have pushed bond yields of Greece, Ireland and Portugal to their highest levels since the introduction of the euro in 1999 amid uncertainty over a second rescue for Athens and the contribution governments are likely to demand from the private sector.

ECB governing council member Nout Wellink told Dutch newspaper Het Financieele Dagblad that a new Greek aid package would carry so many uncertainties and risks that a doubling in the bail-out fund would be necessary to take into account the contagion risk for both Ireland and Portugal.

If you take these risks, you need to build a safety net, Wellink, who is also the outgoing Dutch central bank president, was quoted as saying on Thursday. If it goes wrong, you've got a lot to answer for. If ratings agencies see a rollover (of Greek debt) as a partial default, contagion to other peripheral euro zone countries will occur.

I am open to every variant that does not have consequences in the market, but I know we're skating on very thin ice. If you're at risk of falling through the ice, then you need to have a very big safety net. It should go to 1,500 billion euros and there should be more flexibility in how the money can be spent.

The euro fell to a three-week low of $1.4113 after the report.

Wellink was quoted saying that people should also be prepared to do things the ECB has previously done. This would refer to the ECB purchases of state bonds, the newspaper said.

The ECB is strongly opposed to involuntary contribution from investors. The more risks you take, you must be prepared to create a bigger safety net to prevent contagion. Where the border is between voluntary and involuntary, nobody actually knows, Wellink told the paper.

But if you seek the edges, you need to be aware that you then have the obligation to directly jump in when there are problems.

The European Stability Mechanism (ESM), the new permanent rescue mechanism for the euro zone is due to come into effect from 2013 and will replace the temporary system -- a 750 billion euro emergency loan facility created by the EU and IMF last year.

(Reporting by Aaron Gray-Block; Editing by Ramya Venugopal)