WASHINGTON - US Congressional supporters of a pardon for Jack Johnson, the world's first black heavyweight champion who was imprisoned nearly a century ago for his romantic relationships with white women, say his prosecution was racially motivated.

Johnson made the same argument 90 years ago while in prison.

In a March 25 1921 letter to Harry Daugherty, the attorney-general, Johnson said the prosecutor in his trial made "flagrant appeals to passion, race hatred and moral infamies".

During his 10 months in prison, Johnson sought parole, filed an application with the US president seeking clemency, and wrote letters to the attorney-general seeking early release. And he almost pulled it off.

Daugherty publicly raised the possibility of letting Johnson out a couple of weeks early, before announcing on June 28 1921 - 90 years ago on Tuesday - that Johnson would have to complete his sentence.

Now, under a black president and black attorney-general, the US Justice Department is against pardoning Johnson. In the last session of Congress, both houses passed a resolution urging a pardon pushed by Senator John McCain and congressman Peter King, "to expunge a racially motivated abuse of the prosecutorial authority of the federal government". But US President Barack Obama has not acted on it.

While Obama hasn't commented publicly on the matter, the Justice Department's pardon attorney told McCain and King that the DOJ's resources are best used for pardoning the living. Still, the lawmakers are making another run at the pardon this year.