CHICAGO (AFP) - United States detectives are investigating a tip that on the night gay black actor Jussie Smollett reported being beaten in a hate-motivated attack, he was in a lift with two brothers who were later arrested in the probe.

The 36-year-old star of Fox TV drama Empire told police on Jan 29 that two masked men beat him, yelled racial and homophobic slurs, poured bleach on him and tied a rope around his neck on the streets of downtown Chicago.

Public figures including Emma Watson, Katy Perry, Kamala Harris and Joe Biden led an outpouring of sympathy for Smollett, with Democratic 2020 candidate Cory Booker decrying "an attempted modern-day lynching".

President Donald Trump commented that the alleged attack was "horrible".

Now police say they want to speak to the actor again after two "potential suspects" were released without charge, with US media outlets reporting that the attack may have been staged.

Smollett, who has hired a prominent criminal defence attorney, said his assailants used racial and homophobic slurs and yelled "This is MAGA country" - a reference to Trump's "Make America Great Again" slogan.

But Chicago TV station WBBM reported that the suspects claimed Smollett hired them to stage the attack because he was unhappy that a threatening letter he had earlier received had not got enough attention.

Chicago Police spokesman Jessica Rocco told AFP detectives had received a tip that the suspects were seen with Smollett in the lift of his apartment building on the night of the incident.

Police are working to confirm the tip, said Rocco, who would not reveal whether there was video evidence.

"We do not have any further details at this time," Rocco told AFP.

The suspects were identified as brothers Ola and Abel Osundairo, who had ties to Smollett, according to US media.

The probe could be handed to a grand jury this week, according to the celebrity news website TMZ, which reported on Tuesday that the actor's role on Empire has been curtailed.

Fox declined to comment.