"If you have the ECB which can work in the markets in order to bring down maturities then why not?" Angel Gurria told a news conference during an international business and political conference in Slovenia.

"The system is at stake, the euro should not be put at risk ... the EFSF and the ESM are not enough, fast enough, reactive enough," Gurria added.

He was referring to the European Financial Stability Facility and the European Stability Mechanism, the new, permanent euro rescue fund seen as a key fiscal pillar in Europe's efforts to stem the crisis.

Gurria said he "hoped and expected" Germany's Constitutional Court would approve the ESM on September 12, after it was endorsed by parliament in June. Failure to approve it would almost certainly doom the ESM.

Asked if the ECB should start unlimited bond buying, he said: "Yes, I believe they should, the sooner, the better."

He also forecast the euro zone would remain intact despite the current crisis.

"I believe nobody is going to leave the euro and nobody should leave the euro and I believe some other countries are going to be joining the euro in the future," Gurria said.

He said Slovenia, which markets speculate could become the next country to ask for an international bailout, should focus on reforms and only consider any possible bailout after implementing reforms and reducing the deficit.

"If you (Slovenia) have done everything that you need to do, the banking reform, the state-owned enterprise reform, the pension reform, the labour reform ... and still the markets are attacking than I would say, yes, let's ask the family to help," Gurria said.

(Reporting by Marja Novak; Editing by Zoran Radosavljevic and Alison Williams)

• A Permanent Economic Emergency