Korean Police investigation underway on K-pop star Blackpink photos leak
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It comes after pictures shared on Twitter and Telegram appeared to show the Blackpink star dining with V, from fellow K-pop band BTS.
Rumours have been circulating that the singers are dating.
In a statement, it said it had asked the police to investigate "the original distributor" of the photos, and would take "all possible legal action without any leniency to prevent further damage in the future".
It added: "Photos that were circulated online were illegally released, regardless of the intentions behind them and without the consent of the individual involved".
YG also asked fans to refrain from sharing the pictures more widely.
Two of the accounts associated with sharing the photographs have been suspended.
While YG has not confirmed which pictures it is referring to, several images have spread online that apparently show Jennie and V (real name Kim Tae-hyung) dining together.
One leaker claimed that the photos had originally been posted on a private account, with either Jennie or V writing, "You're my other half" in the caption.
Other photos purportedly show the couple travelling together, and taking selfies in matching Winnie-The-Pooh t-shirts.
None of the images are explicit, although one head-shot allegedly depicts Jennie in the bath.
The stars' faces are partially obscured or blurred in many of the pictures, leading some fans to speculate they are fakes or composites.
BTS's management company Big Hit Music has filed a separate criminal complaint over what it calls defamatory posts containing"false information" and "ill-intentioned rumours" - although it did not specifically name the photos of V and Jennie as the cause of its legal action.
One of the alleged leakers, who posts under the username Gurumiharibo, denied they had been targeted by the entertainment companies.
"I have not received any legal notice from anyone," they wrote in an online chat room. "If somebody wants to sue me for defamation and/or spreading untruths, I will be willing to provide relevant evidence of my claims under the name of the law."
South Korean entertainment companies have recently started taking a hard line against leaks and rumours.
The country's defamation laws allow individuals to be sued for posting defamatory or malicious comments online. They can be found guilty and fined even if their comments are true - as long as it can be proved the statement brought another person into disrepute.
Blackpink and BTS are the most successful of the current wave of K-Pop bands.
Blackpink's recent album Born Pink topped the charts in the US and UK last month, while BTS recently announced a hiatus to work on solo projects.