LAS VEGAS — Mixed martial arts fighter Georges St. Pierre could be disciplined by Nevada athletic regulators after his corner illegally applied petroleum jelly to his body during his Ultimate Fighting Championship title fight against B.J. Penn of Hawaii last week.

Keith Kizer, executive director of the Nevada State Athletic Commission, said Thursday that he entered the ring after the second round of Saturday's welterweight championship fight to instruct the fighter's cornerman to stop putting petroleum jelly on St. Pierre's shoulders and upper back.

Kizer said he and a fight inspector for the commission made St. Pierre's cornermen wipe the jelly from his body.

Under UFC rules, petroleum jelly may be used on a fighter's face, but not elsewhere.

"That's not appropriate," Kizer said.

Kizer said he's not sure whether the jelly affected the outcome of the fight, but said officials are concerned about whether it could have prevented Penn from performing certain grappling moves.

A doctor stopped the fight in the fifth round after a dominant St. Pierre battered Penn. He pressed Penn against the fence in the first round and took him down almost at will throughout the next three rounds. The fight was nearly stopped in the fourth round.

Penn's lawyer, Raffi Nahabedian, told The Associated Press that Penn, a lightweight from Hawaii who relies on grappling to submit opponents using Brazilian jiujitsu, wants a rematch because he believes St. Pierre had the jelly on his body to prevent attempts to grasp him.

"If a ground and pounder can get away with neutralization of a jiujitsu person's game, the sport is corrupt — the sport is fundamentally corrupt and it cannot be considered a fair fight," Nahabedian said. "If it is not a fair fight, then no one should recognize the winner."

Penn's lawyer sent a letter this week, asking the commission to look into the use of the slippery substance. Kizer said the commission forwarded a copy to St. Pierre and asked him to respond within 20 days.

UFC president Dana White was not available for comment because he was traveling, a spokeswoman for the league said. White has said St. Pierre's cornerman — not the fighter himself — is at fault for using the jelly.

St. Pierre's manager Shari Spencer said the Canadian fighter was not cheating, and that the cornerman who applied the jelly accidentally got some on St. Pierre's body while rubbing him during a breathing exercise between rounds.

Spencer said St. Pierre was cooperating fully with the athletic commission and was willing to fight Penn again anytime. St. Pierre won a split decision when the two fought the first time in March 2006.

Kizer said the Nevada commission would likely make a decision at its March meeting, after St. Pierre has responded to its inquiry.

Kizer said disciplinary possibilities include a warning, fines or suspension.