Belgium is leaning on France to pay more into emergency support for failed lender Dexia, newspapers reported, spooking investors who thought a 90 billion euro (77 billion pound) rescue deal only needed rubber stamping.

The countries are wrangling about short-term funding guarantees meant to wean Dexia's bad bank off emergency liquidity and allow it to re-enter financial markets, two Belgian newspapers reported.

Belgium wanted Paris to guarantee more than had been agreed so far, because France can fund itself at a cheaper rate than our country, Belgian daily De Tijd said, following a similar report in De Standaard.

The newspaper did not name its sources.

Both countries on Wednesday denied that the restructuring plan for Dexia was being renegotiated, with Belgian Finance Minister Didier Reynders saying he hoped to reach an agreement with the European Commission in the coming days.

In October, Dexia secured state guarantees from the two countries and Luxembourg for up to 90 billion euros of borrowings over the next 10 years, but talks on the fine print are showing little progress, De Tijd said.

As long as there is no final agreement, Dexia remains dependent on expensive emergency liquidity provided by central banks of about 30-40 billion euros in so-called Emergency Liquidity Assistance (ELA), De Tijd said.

The countries want to get Dexia out of ELA and issue government guarantees instead, ahead of closing a final deal on the 90 billion euro package. The effort is closely overseen by the European Union, according to De Tijd.

They had agreed to share the burden for the interim guarantees in the same way as the October deal, with 60.5 percent falling to Belgium, 36.5 percent to France and 3 percent to Luxembourg.

France struck a very good deal on Dexia ... It would not be surprising that some people within the Belgian apparatus might feel uncomfortable with this, a banker familiar with the rescue of Dexia said.

Re-opening negotiations would be like opening Pandora's box; it could be endless and very dangerous for Dexia's stability, the banker said.

Yields on government bonds rose on the news, and French bank stocks including BNP Paribas and Societe Generale, and Belgium's KBC were among the worst hit in early trading on Wednesday.

If Belgium are unable to carry their load, it puts further pressure on the French government's rating or finances, said Michael Symonds, an analyst at Daiwa Securities.

Shares in Dexia -- worth only a fraction of what they were at the beginning of the year -- rose 10 percent to 0.26 euros. The stock was bouncing after rumours about increased guarantees had hurt it in the past days, a trader said.

Fears about interbank funding spooked markets last week, with unsecured interbank lending practically drying up, and some banks struggling to secure enough collateral to get access to European Central Bank emergency funding.

French Finance Minister Francois Baroin on Tuesday vehemently denied that Belgium had asked his country to renegotiate the Dexia deal.

There are no second thoughts about this accord. All the rest is unfounded or are malign rumours, Baroin said at a news conference on Tuesday.

Belgian Finance Minister Didier Reynders told news agency Belga that none of the three countries was discussing terminating the plan. But the head of Belgium's debt agency spelled out what was at stake.

If the guarantee would be drawn, a full amount, or a partial amount of the guarantee would be put into the budget deficit, and by that means we would have to finance that in the market, too, Anne Leclercq told Reuters.

The European Banking Authority (EBA) has urged banks in Europe to put government guarantee schemes in place to support banks' access to funding where needed.

Dexia's healthy Belgian arm has been sold to the Belgian government, and the company has sold its Luxembourg-based wealth management business Dexia Banque Internationale Luxembourg to Qatar's al-Thani royal family.

It is also holding an auction for its Turkish division DenizBank, with investment bankers saying that HSBC, Standard Chartered and the Qatar National Bank have all put in bids.

(Additional reporting by Sophie Sassard and Simon Jessop in London and Ben Deighton in Brussels; Writing by Douwe Miedema; Editing by Will Waterman and David Cowell)