By Daniel Wiessner and Lisa Richwine

(Reuters) - Former Fox News anchor Gretchen Carlson sued Fox News Channel architect Roger Ailes on Wednesday for sexual harassment, claiming her ex-boss wrongfully fired her after she rebuffed years of unwanted advances.

Ailes, the network's chairman and chief executive officer, denied Carlson's allegations in a statement late on Wednesday. The parent of Fox News, 21st Century Fox <FOXA.O>, said it had begun an internal review of the matter.

Carlson, 50, claimed in a lawsuit that Ailes, a former Republican political consultant who built the Fox News television network into the most-watched U.S. cable news channel, took her off the morning show "Fox & Friends" in 2013 and cut her pay because she refused to have a sexual relationship with him.

Lawsuits alleging sexual harassment typically name the employer as a defendant, but Carlson’s lawyer, Nancy Erika Smith, said in an interview that she had no reason to believe that Fox condoned or authorized the behavior of Ailes.

Ailes was a media consultant for several U.S. Republican party presidents, including George H.W. Bush. He has also been a confidant of 21st Century Fox Executive Co-Chairman Rupert Murdoch, who named Ailes founding chief executive of Fox News Channel in 1996. Fox News remains a subsidiary of 21st Century Fox.

Ailes called Carlson's allegations "false."

"This is a retaliatory suit for the network’s decision not to renew her contract, which was due to the fact that her disappointingly low ratings were dragging down the afternoon lineup," Ailes' statement said.

"This defamatory lawsuit is not only offensive, it is wholly without merit and will be defended vigorously,” Ailes said.

Ailes also said Fox News provided Carlson "with more on-air opportunities over her 11 year tenure than any other employer in the industry, for which she thanked me in her recent book."

The lawsuit filed in New Jersey state court accused the 76-year-old Ailes of wrongfully firing her and before that "ostracizing, marginalizing and shunning her after making clear to her that these 'problems' would not have existed, and could be solved, if she had a sexual relationship with him."

Ailes called her a "man hater" and criticized her for being offended when she had confrontations with former "Fox & Friends" co-host Steve Doocy, the lawsuit alleged.

The lawsuit claimed that Doocy treated Carlson as a "blond female prop", refusing to engage with her on air and belittling her contributions to the show. Doocy was not named as a defendant in the lawsuit.

In a statement, 21st Century Fox said it had seen Carlson's allegations.

"We take these matters seriously," the statement said. "While we have full confidence in Mr. Ailes and Mr. Doocy, who have served the company brilliantly for over two decades, we have commenced an internal review of the matter."

Fox News Channel, known for a lineup of politically conservative commentators that make it popular with Republican party audiences, is drawing record viewer ratings this year. The network was the most-watched channel in all of basic cable television with an average of 2.2 million prime time viewers, according to Nielsen data through June.

Ailes personally intervened when Republican party presidential candidate Donald Trump made disparaging remarks about Fox anchor Megyn Kelly. In January, Fox acknowledged that Ailes had three conversations with Trump ahead of a debate on Fox News Channel which the candidate skipped.

Carlson, in the lawsuit, said her show consistently won the highest ratings in its time slot and achieved its highest ratings ever in the final quarter of 2015 and first quarter of 2016.

The lawsuit said Carlson was fired on June 23. She is seeking damages for lost compensation, damage to her career and mental anguish. A Stanford University graduate and former Miss America pageant winner, she joined Fox News in 2005.

Carlson's lawyer, Smith, said that in the hours since the lawsuit was announced, she had already heard from other women who worked with Ailes and had complaints about his behavior.

In 2005, Fox News agreed to pay $225,000 to settle a lawsuit by the Equal Employment Opportunity Commission that said a former advertising executive sexually harassed a production assistant. A year earlier, "O’Reilly Factor" host Bill O’Reilly paid an undisclosed sum to settle a lawsuit by a former producer who said the top-rated anchor talked to her about sexual fantasies and masturbation.

In a blog on The Huffington Post in June 2015, Carlson wrote that she had been harassed several times early in her career and was speaking out for the first time. "I had no real power, and I was worried that people would blame me or consider me a troublemaker. Sound familiar?" she wrote.

The case is Carlson v. Ailes, New Jersey Superior Court, Bergen County, case number not immediately available.

(Reporting by Daniel Wiessner in Albany, New York; Additional reporting by Lisa Richwine in Los Angeles; Editing by Alexia Garamfalvi, Peter Henderson and Bernard Orr)