Roger Clemens swore under oath Wednesday that he never took performance-enhancing drugs, as his accuser Brian McNamee, who trained the baseball superstar during his time with the Toronto Blue Jays, sat less than a metre away.

"I have never taken steroids or HGH," Clemens told a U.S. Congressional committee. "No matter what we discuss here today, I am never going to have my name restored."

But McNamee, Clemens' trainer from 1997 to 1998, made new accusations.

"I have had that opportunity to think about these events and consider the specific drug regimens we used," he said Wednesday. "As a result, I now believe that the number of times I injected Roger Clemens and Chuck Knoblauch was greater than I initially stated."

The two men were only separated by an investigator who sat between them, and the hearing lasted more than four hours. The Republicans seemed to focus their toughest questions on McNamee, while the Democrats quizzed Clemens.

"It's hard to believe you, sir,'' Rep. Elijah Cummings, a Maryland Democrat, told Clemens at one point. "I hate to say that. You're one of my heroes. But it's hard to believe."

As ranking Republican Tom Davis said of McNamee and Clemens: "Both can't be telling the truth."

The matter may now be referred to the U.S. Justice Department, and it's possible criminal charges could be filed.

McNamee told George Mitchell, a former U.S. senator asked to investigate the use of performance-enhancing drugs, that he had injected Clemens 16 to 21 times between 1998 and 2001.

"I injected those drugs (human growth hormone and steroids) into the body of Roger Clemens at his direction. Unfortunately Roger has denied this and led a full-court attack on my credibility," he said.

"And let me be clear, despite Roger Clemens' statements to the contrary, I never injected Roger Clemens -- or anyone else -- with lidocaine or B-12."

McNamee also said that Andy Pettitte and Chuck Knoblauch of the New York Yankees had used HGH.

Pettitte issued a statement Wednesday that he had used HGH one day in 2004, along with his previous revelation that he had used it in 2002.

In an affidavit for the Congressional committee, Pettitte said that Clemens told him nearly 10 years ago that he used HGH.

Pettitte said in the affidavit that he asked Clemens in 2005 what he would do if asked about performance-enhancing substances, given his earlier admissions.

According to Pettitte, Clemens responded by saying Pettitte misunderstood the previous exchange. Clemens then said he'd been talking about HGH use by his wife Debbie.

But Rep. Henry Waxman, chair of the House Committee on Oversight and Government Reform, noted that McNamee injected Debbie Clemens in 2003. "That makes it impossible that Mr. Clemens, when he spoke to Mr. Pettitte in 1999 or 2000, could have been referring to these injections of Mrs. Clemens," he said.

Clemens told the committee Wednesday that Pettitte must have "misremembered."

Waxman said there were reasons to doubt the credibility of both McNamee and Clemens.

Criminal charges could conceivably be laid if Clemens, a seven-time Cy Young award winner, is shown to be lying.

Clemens did get some help in an affidavit from another ex-teammate.

"I have never had a conversation with Clemens in which he expressed any interest in using steroids or human growth hormone," Jose Canseco said in a sworn affidavit, dated Jan. 22, that was submitted to the committee.

"Clemens has never asked me to give him steroids or human growth hormone, and I have never seen Clemens use, possess or ask for steroids or human growth hormone."

Canseco's book "Juiced," about steroids in baseball, led to Congressional hearings in 2005.

With files from The Associated Press