Backstreet Boys' Nick Carter Countersues Woman Accusing Him Of Sexual Battery

Nick Carter says the woman accusing him of sexual battery over 21 years ago -- when she was a minor -- is deliberately dragging his name through the mud with a series of lies ... and he's now going after her in court for the more than $2.35 million he says she's cost his boy band.

The Backstreet Boys member filed his countersuit Thursday against Shannon Ruth. TMZ broke the story, Ruth initially sued Nick in December, claiming he sexually assaulted her after a concert way back in 2001 when she was underage.

In new legal docs, obtained by TMZ, Nick says he won't allow himself to be smeared by Ruth's accusations, which he vehemently denies, and says her lawsuit is the culmination of a years-long conspiracy to take him down.

Nick says Ruth has been coached by a father and daughter, Jerome and Melissa Schuman, to make false claims about him as part of an extortion attempt. He also blasts all 3 for trying to take advantage of the #MeToo movement.

Carter says Ruth has changed her story over and over ... he says she initially claimed she was abused by someone else, then claimed Nick physically abused her, and ultimately accused Nick of sexual assault. Nick says the Schumans have been "coaxing" Ruth to "inflate" her allegations.

Nick points out Ruth waited years to report her sexual battery allegations, and he says an independent investigation resulted in no criminal charges. He says Ruth tried to extort him through civil attorneys, who abandoned her case when presented with the cold, hard facts.

Nick says as a result of Ruth's lawsuit, The Backstreet Boys had to cancel appearances and endorsement deals -- costing them more than $2.35 million.

And get this -- Nick says his late brother, Aaron Carter, was also dragged into the conspiracy. Nick claims Ruth and the Schumans preyed on Aaron before his death, when he was beefing with Nick and on drugs, exploiting "Aaron's fragile condition and family stresses to cloak their defamatory campaign with credibility, relentlessly and repeatedly using Aaron to try to legitimize their frivolous tales."

But, Nick says Aaron ultimately realized he was being used and manipulated by Ruth and the Schumans, apologizing to Nick and publicly stating the accusers were lying.

The day Aaron died, Nick claims Jerome Schuman tweeted ... "I am sad that the chess game we started together was never finished."

When TMZ called Nick’s attorney, Michael Holtz, he told us, "As our Counterclaim sets out in detail, Nick has been the target of a malicious and long-running conspiracy. He has never done the outrageous things of which he has been accused; in fact, he is the victim of a calculated and concerted disinformation campaign designed to destroy his reputation."

Holtz continues, "He looks forward to setting out the truth, vindicating himself in court, and putting an end to the smears and attempted shakedowns for good."