Federal prosecutors in Manhattan said on Friday that Iranian plotters had discussed a plan to assassinate Donald J. Trump before he was re-elected as president this week.

One of the plotters said that he was assigned in September to carry out the plan by the Islamic Revolutionary Guards Corps of Iran, the prosecutors said in court papers.

An Iranian operative said he was told to put aside other efforts he was undertaking on behalf of the Revolutionary Guards and “focus on surveilling, and ultimately, assassinating” Mr. Trump, according to a criminal complaint filed in Manhattan federal court.

The operative told a Revolutionary Guards Corps official that such a plan would cost a “huge” amount of money, the complaint said. In response, the official said, “We have already spent a lot of money,” adding that “money’s not an issue.”

The newly filed complaint also contains allegations that the authorities had disrupted another plot to assassinate Masih Alinejad, a Brooklyn human-rights activist who has long criticized Iran’s repression of women.

This is a developing story and will be updated.