Terrorist groups and drug traffickers are using anonymously owned U.S. shell companies to hide and move their money, a senior Treasury official warned Tuesday, calling on Congress to crack down.

"With every threat that we track, be it foreign terrorists, narcotics cartels, sanctioned regimes or cyber hackers, our investigators encounter American shell companies used to hide and move money," wrote Adam Szubin, the acting under secretary for terrorism and financial intelligence, in an opinion article.

"A loophole in our financial system allowed for this secrecy, and it took years to uncover the full money trail," he wrote in The Hill, a specialized publication on congressional affairs.

The Treasury proposed to Congress last month legislation that would require the beneficial owner of a company to be identified whenever a U.S. company is formed.

Currently a number of states officially permit companies to be formed and registered with their beneficial owners remaining anonymous.

"This gives U.S. shell companies the dubious distinction of being the only money laundering method where secrecy is provided by a government entity," Szubin wrote.

He recalled that stopping terror financing and money laundering have been broadly supported by Congress, but over the years "interested stakeholders" have systematically defeated legislation similar to the Treasury's recent proposal.

"This is simply unacceptable."

The United States and other major countries have stepped up a global effort to end tax evasion and money laundering, especially after the release of the "Panama Papers" that exposed the widespread use of shell companies.

In mid-April, the Group of 20 economic powers, including the US, recommended the adoption of measures to improve financial transparency and tackle loopholes such as shell companies.