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Washington (CNN) -- Sen. Robert Menendez, who has been dogged by a federal corruption probe, suggests he was the target of a Cuban intelligence smear plot over allegations -- which the FBI has discounted -- that he had sex with underage prostitutes in the Dominican Republic.

The New Jersey Democrat told CNN in an exclusive interview on Tuesday that the Justice Department should look at any evidence it may have that he was the subject of a conspiracy by the regime to spread false allegations.

Menendez said he has for years had a "firm position in opposition to the Cuban regime" on grounds that it violates human rights.

"The democracy of the people of Cuba -- I have been outspoken in that regard, and I wouldn't be surprised that the regime would do anything it can to stop me from being in a position that ultimately would impede their hopes of getting a different relationship with the United States based upon their interest not the interest of the American people," he said.

A U.S. law enforcement official told CNN later Tuesday that investigators have been aware of Menendez's allegation about the Cuban intelligence smear for some time. Moreover, they have found no evidence to support the claim that Cuba tried to smear the senator.

Menendez: Cuba may have spread smear story

From his perch as chairman of the Senate Foreign Relations Committee, Menendez has pushed the Obama administration to hold the line on sanctions against the regime of Raul Castro.

The Cuban Interests Section in Washington didn't immediately respond to a request for comment.

But an article posted on the Cuban government-run website Cubadebate denied Menendez's allegations.

"The senator's strategy is nothing more or less than to blame Cuba, an old recourse of counter revolutionary Cuban politicians to wash away their failings," it said.

The story added that the Cuban government has "no ties" to the Daily Caller which first reported the prostitution story.

FBI found no merit in claim

It's a dramatic twist to an already sensational story. The FBI found no merit in the prostitution angle when it investigated previously.

But the latest development may complicate an ongoing federal corruption probe of Menendez. His comments on Cuba amount to a legal Hail Mary.

Authorities are investigating his relationship with political donors, including one whose ophthalmology practice in Florida has been scrutinized for its billing practices.

The Washington Post first reported the latest turn in the story Monday night, saying the suggestion of a Cuban smear is based on a CIA finding that Cuban intelligence agents were behind the prostitution claims.

The CIA declined to comment.

Such a formal finding by the agency would be unusual -- though not unheard of -- because the FBI, not the CIA, has primary responsibility to investigate foreign intelligence operations against a U.S. government official.

A person familiar with the Menendez legal strategy said his attorney, Stephen Ryan, asked the Justice Department in a letter to investigate the Cuba situation.

Menendez called any suggestion that he was trying to create a diversion or check the federal corruption probe with his Cuba comments a "pretty far-fetched idea."

But he said that it "seems to me" the government "has the proof," based on the Washington post reporting.

"As far as I am concerned, you know, it is the government that should produce the information that they supposedly have within their own agencies," Menendez said.

If the CIA finding is true, the person said, then the corruption probe would be tainted by the fact Menendez was a victim of a foreign intelligence smear.

2013: Sen. Menendez faces scrutiny over ties to Florida doctor

Tipster triggered probe, stories

The episode began in April 2012 when a tipster alerted the Citizens for Ethics and Responsibility in Washington, a watchdog group, that he had evidence Menendez engaged in sex tourism by traveling to meet underage prostitutes in the Dominican Republic.

An FBI agent in Miami attempted to run down the tip, but nothing materialized. The tipster wouldn't provide additional information or talk to the agent, according to e-mail records forwarded to media. The purported prostitutes also recanted their claims.

At the time, Menendez was ascending to the top foreign affairs committee post in the Democratic-controlled Senate.

The FBI's foray into that allegation dovetailed with the wider, ongoing federal investigation focused on the Florida donor, who for years has fought allegations that he overbilled Medicare.

The FBI's investigation is also examining efforts by Menendez to advocate on behalf of two Ecuadorian brothers, whose family members are political donors to him and who are fighting extradition to their homeland to face embezzlement charges.

People familiar with the investigation say the overall probe continues, with the FBI and prosecutors still examining whether Menendez broke any laws in his ties to political donors.

Lawyer: Senator and Dominican prostitutes story cooked up by Cuban intelligence agents

2013: Dominican police: Women were paid to lie about Sen. Robert Menendez

2013 Report: DEA agents made prostitute arrangements for Secret Service agent

CNN's Evan Perez and Patrick Oppmann contributed to this report.