Five years after the worst of the financial crisis, the world has not yet come close to building a "harmonized, robust" market for over-the-counter swaps, a top U.S. Federal Reserve official said on Thursday.

New York Fed President William Dudley said in a speech he is concerned that OTC derivatives reforms have been delayed and will fall short of a broader revamp of financial markets in the post-crisis era.

The Basel Committee of regulators and central bankers are forcing the mandatory clearing and on-exchange trading of OTC contracts where possible in the 20 leading economies, or G-20, and for all transactions to be recorded.

Last week, new rules meant to make the $630 trillion market safer were eased to avoid harming economic activity, as some banks have argued.

Despite the slow progress, Dudley said regulators may need to push even harder to ensure enough derivatives become "standardized" and freely traded as opposed to "bespoke." As well, the venues that clear the trades, known as central counterparties, must comply with all global rules, and so-called trade repositories must have all trading data available.

"The OTC derivatives reform effort fits in very well with the broader reform agenda, but there are significant risks that we will fall short in this arena relative to what we are likely to achieve elsewhere," he said in prepared remarks to a derivatives conference in Paris.

Dudley, whose branch of the Fed directly oversees Wall Street, acknowledged that swaps rules are more difficult to implement than bank-capital rules, for example.

But as it stands, he said, the Fed and other regulators cannot determine the amount of risk that remains in the system, or how secure is its infrastructure.

Regulators want to apply lessons from the 2007-09 financial crisis in which the opaqueness of derivatives such as credit default swaps — used to insure against falls in bond prices — badly exacerbated market uncertainty.