(Updates with reports of earlier probes)

WASHINGTON, Feb 18 (Reuters) - The U.S. Federal Bureau of Investigation and others have been investigating whether Texas billionaire Allen Stanford was involved in laundering drug money for Mexico Gulf cartel, ABC News reported on Wednesday, citing federal authorities.

The U.S. Securities and Exchange Commission on Tuesday charged Stanford and two executives of Stanford Group Co with an $8 billion fraud.

Mexican authorities detained one of Stanford’s private planes as part of the investigation, which has been ongoing since last year, ABC reported, citing unnamed officials.

Officials said checks found inside the plane were believed to be connected to the Gulf cartel, reputed to be Mexico’s most violent gang, ABC reported.

FBI spokesman Richard Kolko said the agency could not confirm or deny an investigation.

ABC cited authorities as saying that Stanford could potentially face criminal charges of money laundering and bribery of foreign officials.

Authorities said the SEC’s action against Stanford on Tuesday may have complicated the federal drug investigation.

The SEC investigation follows earlier government probes into Stanford’s payment of federal taxes and his offshore businesses, The Washington Post reported in Thursday editions.

The FBI and other federal agencies launched multiple investigations into suspected money laundering at Stanford’s offshore banks in the 1990s but could not come up with evidence to charge him, the Post reported, citing a former federal law enforcement official.

Industry experts say significant securities violations at Stanford Group years before this week’s SEC move were telltale signs of deeper problems, The New York Times reported. Records show that each time regulators ultimately let the company off with relatively small fines, the paper said.