Smokey Robinson Under Criminal Investigation for Sexual Assault

12:22 PM PT -- Smokey Robinson's attorney Christopher Frost tells TMZ ... "We are aware that a police report has now been filed by the Plaintiffs in the civil lawsuit. It is clear to us what is happening here. Plaintiffs filed a police report only after they filed a $50 million lawsuit. This means only that the police are now required to investigate. We welcome that investigation, which involves Plaintiffs who continue to hide their identities, because exposure to the truth is a powerful thing."

He adds ... "We feel confident that a determination will be made that Mr. Robinson did nothing wrong, and that this is a desperate attempt to prejudice public opinion and make even more of a media circus than the Plaintiffs were previously able to create. The record will ultimately demonstrate that this is nothing more than a manufactured lawsuit intended to tarnish the good names of Smokey and Frances Robinson, for no other reason than unadulterated avarice."

Smokey Robinson is now the subject of a Los Angeles County Sheriff's Department investigation after multiple women came forward and filed police reports alleging sexual assault ... TMZ has learned.

Law enforcement sources tell TMZ ... three alleged victims -- all female -- filed police reports against Smokey on Friday with the sheriff's department. The department's special victims' unit has opened a criminal investigation into the claims. We're told the investigation is in its early stages.

Our sources say investigators will reach out to Smokey to try to speak to him about all the allegations made against him in these police reports.

John Harris and Herbert Hayden, the attorneys representing the 3 women, tell us they are "pleased to learn that the L.A. County Sheriff's Dept has opened a criminal investigation into our clients' claims of sexual assault against Smokey Robinson. Our clients intend to fully cooperate with LASD's ongoing investigation in the pursuit of seeking justice for themselves and others that may have been similarly assaulted by him."

As you know ... four Jane Does -- all of whom claim they used to work as housekeepers for Smokey -- filed a lawsuit against the star earlier this month, alleging sexual battery, assault, false imprisonment and gender violence, seeking millions in damages.

In the lawsuit, the four accusers claim they were sexually assaulted by Robinson multiple times. All of them claim Smokey would call them into his bedroom or other places while his wife was away from the house, where he would then force himself upon them.

Smokey's attorney called the civil lawsuit an attempt to "extract money from an 85-year-old American icon" and called all of the allegations totally false.