Greece is far from stabilizing its finances and should restructure its sovereign debt, the head of the world's biggest bond fund wrote in an article for German daily "Handelsblatt" on Wednesday.

"So far none of the solutions for the Greek debt crisis have worked. And a lot of people — including me — don't believe that they will work in the future," Mohamed El-Erian, chief executive of Pacific Investment Management Company (Pimco), wrote.

Greece will need "a preferably voluntary and orderly restructuring" to relieve itself of its debt burden, the Pimco CEO said.

He said that Greece's rescue by the European Union, the ECB and the International Monetary Fund (IMF) had not brought the results that were hoped for and called for urgent improvements.

"This means abandoning rescue attempts if they do not and will not work," El-Erian said.

El-Erian admitted though that efforts so far have reduced the risk of contamination for other countries and institutions.

But a debt crisis could not be resolved by simply enhancing liquidity, he said: "Just adding new debt to the bulk of already existing debt is not a long-term solution."

Speculation that Greece would have to renegotiate its debt with creditors somehow has grown despite warnings from many policymakers that such a move would have catastrophic consequences.

ECB Governing Council member Athanasios Orphanides said on Wednesday that Greece has made significant progress in implementing an EU/IMF austerity program and any suggestion of restructuring its debt would be wrong.