Law enforcement sources tell us the 3 people were charged Thursday, and at least one of the suspects worked at the CasaSur Palermo Hotel, where Liam died.

We're told one suspect is described as a "friend" who was in Liam's hotel room with him, but left him there at some point before he died. That suspect has been charged with abandonment of a person before death.

The second suspect is a hotel housekeeper, who police believe likely delivered drugs to Liam in a soap box. As we reported, cops had been eyeing the Dove soap box found in the room, because only housekeeping staffers have access to that soap supply within the hotel.

We're told the third suspect is the alleged drug supplier, who prosecutors say delivered narcotics to Liam twice on October 14 ... 2 days before his death. The alleged dealer and the hotel staffer are both facing charges for dealing.

Prosecutors say they combed through more than 800 hours of hotel surveillance video after conducting multiple raids at the hotel, and at homes around Buenos Aires.

This update comes 3 weeks after the 31-year-old One Direction singer fell to his death from a third-floor balcony at the hotel.

As TMZ previously reported, the singer had been in Buenos Aires to support former bandmate Niall Horan's show at the Movistar Arena earlier in October ... choosing to extend his trip with girlfriend Kate Cassidy by his side.

However, his visit took a tragic turn after Kate, an American influencer, chose to return to the States without Liam ... leaving the singer to stay in Argentina's capital city alone.

LP was acting erratically before falling from his hotel balcony ... with an initial autopsy report finding cocaine, crack, ketamine, ecstasy and a form of crystal meth, called "cristal," in his system.

We broke the story ... investigators began looking at hotel employees in the aftermath of Liam's death -- one worker allegedly had given the British star anti-anxiety medication, which was found in his room.

Photos from Liam's hotel room showed a chaotic scene ... drugs and paraphernalia were notably found among his belongings. Liam had previously opened up about his addiction struggles ... confirming in July 2023 that he was sober after a stint in rehab.

Liam's father, Geoff, was in Buenos Aires for a time to help investigators looking into his son's death.