A top oil executive and adviser to Donald Trump said the Republican presidential nominee has changed his mind on his support for local fracking bans.

In an interview with the Wall Street Journal, Harold Hamm, the chief executive of Continental Resources Inc., said Trump no longer supports local and state fracking bans. Trump said in a July interview with a Colorado TV station he "can understand" if cities and states want to ban fracking.

Hamm told the paper he didn't actually speak to Trump about his comments, but he was sure that he has changed his mind.

"Donald Trump did not understand that concept at the time in my opinion," Hamm told the Journal. "He does now."

In July, Trump ruffled Republican feathers when he said the will of voters should be respected if they wanted to ban fracking. Two cities in Colorado had voter-passed initiatives to ban or halt fracking shot down by the Colorado Supreme Court because they conflicted with state law.

When asked if he supported cities or states making their own decisions on banning fracking, Trump said it's up to the voters.

"I'm in favor of fracking, but I think voters should have a big say in it," Trump said. "I mean, there's some areas that maybe they don't want to have fracking and I think if the voters are voting for it, that's up to them."

But Hamm told the Wall Street Journal that Trump was caught up in the idea of "local control" instead of sticking to the party line on energy production.

"I think he was pulled into that with the term 'local control,' which is a magnet for Republican thoughts," Hamm said.