A South Carolina law enforcement official said he would charge Phelps if he could prove the US Olympian smoked marijuana in his county.

“This case is no different than any other case,” Richland County Sheriff Leon Lott told The State.

Lott's comments come after a British newspaper published a photograph purportedly showing Phelps smoking marijuana at a party being held by students at the University of South Carolina in Columbia in November.

Columbia, the South Carolina state capital, is located in Richland County.

“This one might be a lot easier since we have photographs of someone using drugs and a partial confession. It's a relatively easy case once we can determine where the crime occurred.” Phelps apologised on Sunday after publication of the photograph by the News of the World, calling his behaviour “inappropriate.” Both the University of South Carolina and Columbia police departments have said they would not pursue charges against Phelps, The State said.

The International Olympic Committee (IOC) said it accepted his apology and U.S. officials said the news was disappointing but stressed that smoking marijuana out of competition was not an anti-doping matter.