US and European regulators are still at loggerheads on how to harmonise new rules overseeing the $600 trillion derivatives landscape, threatening activity across the world's two largest swaps markets.

The impasse has returned to the fore after Jonathan Hill, European Commissioner for financial stability, and Timothy Massad, chairman of the US Commodity Futures Trading Commission, failed to reach an agreement in Brussels on May 7 on the 'mutual recognition" of each region's clearing rules.