The tougher rules, known as Basel III, are the world's regulatory response to the 2007-09 financial crisis and would force banks to triple the amount of basic capital they hold in a bid to avoid future taxpayer bailouts.

The European Banking Federation sent a letter on November 21 to EU Commissioner Michel Barnier, formally requesting a delay on the grounds that EU banks would be at a competitive disadvantage if they introduced the new rules before their U.S. counterparts.

"We are now very troubled over the possible repercussions that the most recent statement from the US Authorities may have for the international competitiveness of Europe's banks," the letter, made available to Reuters, said.

It said EU banks were facing sweeping regulatory changes including new rules on capital requirements and liquidity buffers, and the creation of a EU supervisory authority.

"All the while, our US competitors will not have matching obligations imposed on them in parallel, or in a foreseeable future," it said, asking for the introduction of the new rules to be delayed to January1, 2014.

The Basel III rules are meant to be phased in from January 2013 but U.S. regulators cast doubt on the timeframe due to a flood of industry comments on the proposals.

"Basel III must be postponed, full stop" said the head of Italy's banking association, Giuseppe Mussari, at a conference in the central Italian town of Gubbio.

"Clearly there is no worldwide agreement, so we wouldn't be starting on a level playing field."

(Reporting By Giselda Vagnoni, writing by Silvia Aloisi, editing by William Hardy)

• A Permanent Economic Emergency