Top U.S. regulators told a Congressional committee on Tuesday that there are many problems with the way cryptocurrency markets operate and that tighter regulation and a more coordinated response between federal agencies is needed to protect investors.Securities and Exchange Commission Chairman Jay Clayton said he is very unhappy that people are conducting ICOs like public offerings of stock and added that regulators may ask Congress to pass legislation to improve oversight of digital currencies.But in a week of plunging prices and bad news the testimony was not as negative as many cryptocurrencies investors had feared.Commodity Futures Trading Commission head Christopher Giancarlo acknowledged that the blockchain ledger technology underpinning digital currencies had made a positive contribution to the modern financial system.Both chairmen said that while they had limited authority to police the cryptocurrency market they would use their enforcement powers aggressively to protect investors from fraudsters.