Justin Bieber Tells Late Liam Payne to 'Rest Easy' After Death

Justin Bieber is thinking of Liam Payne and his fans in the days following the One Direction alum's death ... encouraging those who love the singer to grieve as they see fit.

The pop star posted on his Instagram Stories Monday, where he addressed Liam's passing by sharing a fan video featuring the many vigils assembled in LP's honor.

A caption on the clip read ... "Rest Easy Liam."

The video was accompanied by a poignant voice-over, which encouraged Liam's fans to mourn the loss of the 1D star, even if they've never met him.

The clip noted ... "Just remember: you are allowed to grieve as a fan. You are allowed to love someone you've never met. You are allowed to admire someone for their art. You are allowed, to cry, to break, to feel like a part of you is gone."

Justin appeared to co-sign this sentiment by sharing the video on his social media ... joining the countless other celebrities who've paid tribute to LP this last week.

As TMZ previously reported, Liam was pronounced dead at the CasaSur Palermo Hotel in Buenos Aires, Argentina last Wednesday after he fell from a third-floor balcony. Police have stated that Liam jumped ... noting drugs may've played a role in his possible suicide -- the investigation is ongoing.

Initial results from the singer's autopsy show multiple substances were in his system before he died ... including a mix of drugs known as "pink cocaine." Not only were cocaine and crack found in his body when he fell to his death, but we're told "Cristal" -- Argentina's version of methamphetamine -- was also detected, along with other hard drugs.

Liam had been in Buenos Aires supporting former bandmate Niall Horan's gig at the Movistar Arena earlier this month ... ultimately extending his trip, which was originally supposed to be only 5 days long.

Liam is survived by his 7-year-old son, Bear ... who he shares with ex Cheryl Cole.

He was 31.