A wave of racist text messages summoning Black people to report for slavery showed up on phones across the United States, prompting the scrutiny of the F.B.I. The N.A.A.C.P. said that messages were received in nine states, and attorneys general in two other states reported the same on Thursday, two days after the presidential election.

The F.B.I. said in a statement that it was “aware of the offensive and racist text messages” and that it was coordinating with the Justice Department and other federal authorities.

The texts, which began as early as Wednesday morning, were reported across the South, and from New York to California. The office of the New York attorney general, Letitia James, said the messages had arrived in phones of middle school, high school and college students in New York City and its suburbs. In a statement, Ms. James called the messages “disgusting and unacceptable.”

Some examples of the messages were shared by recipients and reviewed by The New York Times. They followed a pattern: addressing recipients by name, telling them they had been selected to “pick cotton” on a plantation and ordering them to show up at a specific time to be picked up by slave handlers. Some included a reference to the president-elect, Donald J. Trump.

A spokesman for the Trump campaign, Steven Cheung, said in an email that the “campaign has absolutely nothing to do with these text messages.”

Mr. Trump stoked racism throughout his campaign in speeches that included false accusations against immigrants and inflated crime figures. He demeaned the intelligence of his opponent, a Black woman; repeatedly amplified a lie that Haitian immigrants were eating neighbors’ pets in Ohio and held a rally near the end of his campaign at Madison Square Garden that was rife with bigotry and misogyny.

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