Three sources familiar with the matter told Reuters on Monday the United States is expected to impose the sanctions as early as next week, coinciding with the one-year anniversary of what may have been the bloodiest repression of protesters in Iran since the Islamic Revolution in 1979.
Iran's judiciary spokesman Gholamhossein Esmaili said the 157 "security detainees" were among 2,301 people freed under a pardon by Supreme Leader Ayatollah Ali Khamenei as part of events marking the anniversary of the birth of the Prophet Mohammad, state media reported.
The 157 suspects had been convicted of "propaganda against the system, (illegal) assembly and collusion, and taking part in riots" after being arrested in anti-government protests in recent years, the spokesman said.
Rights groups estimate that thousands were arrested in the 2019 protests, which broke out over gasoline price hikes and quickly turned political, with protesters demanding that top officials step down.
The sources said the sanctions had been in the works for months and were the latest in a long series of U.S. penalties imposed on Tehran by U.S. President Donald Trump after he withdrew from Iran's 2015 nuclear deal with world powers in 2018.