Two Thai cops are under investigation for partying with a rock star shortly after he was bailed on gun charges, police said Friday, a scandal illuminating the kingdom's culture of impunity for the rich and famous.

The two police colonels from Nakhon Si Thammarat province came unstuck after social media images emerged of them at a raucous dinner on January 3 with the popular musician known as Sek Loso.

The rocker, whose bad-boy antics are a fixture of Thai gossip columns, had just been released on bail after a video clip of him firing a pistol into the air outside a Buddhist temple went viral.

The incident took place on December 28 in the area of Nakhon Si Thammarat under the command of the pair of policemen.

Sek racked up more charges a few days later after he again whipped out a gun in a stand-off with cops at his Bangkok home on December 31, after which he was arrested.

But the bad blood didn't last for long, with Sek describing the two police officers as "brothers" in the caption of an Instagram photo showing the group dining out on the night of his release.

A third senior cop in Bangkok also raised eyebrows for taking a "thumbs-up" photo with Sek inside a police station, which the singer then posted on Instagram with the caption "thank you superintendent... whom I owe thanks to for making everything easier."

For ordinary Thais, the chummy photos have provided a fresh window into a justice system that critics say is warped by privilege and allows the kingdom's wealthy and well-connected to escape serious punishment.

All three cops have been transferred pending a probe into whether their "actions broke police discipline", according to statement by police spokesman Krissana Pattanacharoen.

The national police chief has commanded all officers "not to act in a way that could lead to public misunderstanding that police have close personal relationships with suspects," Krissana added.

But Thais are well-versed in tales of close bonds between cops and wealthy suspects.

The heir to the Red Bull fortune, Worayuth Yoovidhya, skipped the country last year to evade a belated arrest warrant linked to a deadly hit-and-run with his Ferrari in 2012.

Police were pressured into issuing an arrest warrant for the scion, whose billionaire father is Thailand's fourth-richest man, nearly five years after the incident.

On Thursday, Sek tired to defuse anger over accusations of special treatment, posting a photo of himself from his time behind bars with the caption:

"Jailhouse rock! If you think I have been privileged over other people, look at these two pictures, the police have done their best. I ask you to stop reprimanding all sides."