Mitt Romney is likely to run for the Utah Senate seat vacated by Orrin Hatch's retirement, a source told CNBC.

A source who has long been close to Romney believes the former Massachusetts governor and Republican presidential nominee will run for Senate later this year. Separately, NBC News reported that Romney wants to seek the Senate seat, citing a person familiar with his thinking.

Romney, 70, has been one of the harshest Republican critics of President Donald Trump. He is popular in Utah, the state where he now lives.

The former governor has slammed some of Trump's public comments and taken different stances from him on some foreign policy issues, particularly the U.S. relationship with Russia. However, he has long pushed for conservative economic principles.