Donald Trump said he is not ready to pardon longtime friend and political adviser Roger Stone, saying he wants the legal process to "play out."

The president said the forewoman of the jury was biased, and said his former adviser is a good candidate for "exoneration."

"I want to address today's sentencing of a man, Roger Stone. I'm following this very closely and I want to see it play out to its fullest because Roger has a very good chance of exoneration in my opinion," he said during a speech to former convicts in Las Vegas.

Roger was never involved in the Trump campaign for president. Early on, before I announced, he may have done a little consulting work or something," Mr Trump said. "He's a person who knows a lot of people having to do with politics. It's my strong opinion that the forewoman of the jury ... is totally tainted."

"Roger has a very good chance of exoneration, in my opinion," he added.

During his speech, Mr Trump told the graduating class of a program to help former inmates transition to civilian life, "We believe in second chances" and slammed "bad juries."

"I'm not going to do anything with the great powers bestowed upon the president of the United States," he said, adding he wants "to see the process play out."

The president's remarks amounted to a partial rebuke of the justice system, describing it as too corrupt.

"You wouldn't know about a bad jury. Anybody here?" he said, smiling as the group stirred and laughed and cheered.

"You're my experts, OK," he said. "How can you have a jury pool tainted so badly?"