The head of Europe's bailout fund was reported on Sunday as saying he wants to boost state guarantees on the fund's bonds, although a fund official said no changes had been made to an original plan.

Without citing its sources, German newspaper Bild am Sonntag had said Klaus Regling wanted to increase guarantees to up to 30 percent for investors outside the euro zone. A fund official said that the figure had already been mentioned.

The comments from Regling... should not be interpreted as a deepening of the (debt) crisis, the official from the European Financial Stability Facility said, underlining that state guarantees had always been planned to range from 20-30 percent.

The guarantees aim to provide incentive for nations with big foreign reserves, such as China, to invest in leveraging the fund's lending capacity, despite their initial cool response late last year.

In its report, Bild am Sonntag said that Regling had described a 20 percent guarantee as insufficient at a meeting of Bavarian conservatives last week.

The EFSF plans for the leveraged fund to be fully operational this month. But concerns of a euro zone default could also make plans to offer first-loss bond insurance -- a pillar of the EFSF's leveraging plan -- too costly.

Providing insurance on more than the first 20 percent of euro zone bonds in the case of default would eat up the 250 billion euros the EFSF has left -- after lending to Ireland and Portugal -- and aims to multiply.

Last week, the EFSF looked to have overcome weak demand in a previous auction when it sold an oversubscribed 3 billion euros ($3.8 billion) worth of bonds to raise funds for cash-strapped Ireland and Portugal.

The Luxembourg-based fund, set up in 2010, is hoping that strong demand will quieten concerns that it could struggle to raise funds as the debt crisis threatens the credit ratings of its main guarantors, particularly France.

Also in its Sunday edition, Bild am Sonntag said that the German government was considering a plan to speed up the activation of the EFSF's successor, the European Stability Mechanism, as a way to send a clear signal to the markets.

It said the debate focused on whether governments should fund the 80-billion-euro strong mechanism in one go instead of via five tranches over several years as originally planned.

Also conceivable is the idea of using state funds to increase the size of the ESM to 100 billion euros, the paper wrote, citing unnamed sources in the German government.

The ESM, designed to take over from the EFSF as a permanent bailout mechanism, is likely to be discussed when French President Nicolas Sarkozy meets German Chancellor Angela Merkel in Berlin on Monday.

(Writing by Brian Rohan, additional reporting by Ilona Wissenbach. Editing by Jane Merriman)