Agreeing tough new bank capital rules must be top priority in global efforts to learn from the financial crisis, finance ministers from the G20 group of countries will be told later this week, sources said on Tuesday.

The group of leading developed and emerging market countries will gather on the sidelines of an International Monetary Fund meeting in Washington on April 22-23.

The IMF and the Financial Stability Board (FSB), tasked by the G20 to coordinate implementation of regulatory reform, will present a joint report to the finance ministers on how to deal with too big to fail banks.

The main message coming through this document from central banks and regulators is that priority number one is Basel III, while the practical study of a bank levy should come after the results from the study on the impact of Basel III, two sources involved in the G20 process said.

The IMF and FSB fear that otherwise discussions on a bank levy could sap political momentum on Basel III, the sources added.

The G20 has agreed to introduce Basel III -- a much tougher version of the existing Basel II global accord on bank capital requirements -- by the end of 2012.

Banks are pushing for a watering down of some elements and delaying its implementation, saying that otherwise economic recovery could be threatened.

The IMF-FSB report will say the Basel Committee on Banking Supervision, which drafted Basel III, is also studying possible capital surcharges on large, risky banks.

The two bodies want the Basel Committee to complete this work before the G20 take any decisions on whether to also impose a separate levy or tax on banks to pay for bailouts, the sources said

There is no trade off between surcharges and a levy, they could go be introduced together if combined in the right way, the sources added.