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MIAMI (CBSMiami) — Senator Marco Rubio may be the target of an assassination plot by a senior official within the Venezuelan government of Nicolas Maduro, according to a memo distributed by U.S. intelligence officials and obtained by CBS4 News.

The memo refers to the information as “a potentially grave threat to Senator Rubio.”

The unverified warning prompted federal officials to increase the security around the Florida Republican leading to the ongoing, round-the-clock protection for him and his family.

“You have to take this as serious and credible given the information,” a law enforcement source who had been briefed on the threat told CBS4 News. “We have no other choice.”

The threat and the memo were first reported Sunday afternoon by The Miami Herald.

The memo detailing the threat traces the origins of the plot to Diosdado Cabello, the head of that country’s ruling political party who is also suspected of controlling the Venezuelan military.

The memo describes the information as “reliable and credible” but draws no conclusion on whether the threat is real. The two-page memo is marked “law enforcement sensitive” but is not classified. The memo includes highly confidential information that is not typically included in reports that will be widely distributed – even within law enforcement agencies. CBS4 News has agreed not to post the memo online or release its more sensitive subjects.

During a Senate Foreign Relations sub-committee hearing last month on the future of Venezuela, Rubio took aim Cabello, accusing him of cementing Venezuela’s role as a major drug trafficking hub.

“There are also very strong allegations made by some people about the role of Diosdado Cabello, an individual who, in my perspective, based on everything I have seen, is not simply a drug-trafficking leader,” Rubio said. “In my opinion, he is the Pablo Escobar of Venezuela.”

Rubio went on to say: “He is a very dangerous man.”

Cabello denies he is involved in drug trafficking.

The increased security around Rubio started three weeks ago while he was in Washington but it became even more noticeable when he returned to Miami for the August congressional recess. During a visit to CBS4’s newsroom in early August to discuss the recent election in Venezuela as well as other issues, Rubio was accompanied into the building by three, plainclothes Capitol Police officers while Miami-Dade police closed down the street in front of the station. Rubio did not have that level of protection when he ran for President last year.

It is not uncommon for members of Congress to receive threats or have additional security assigned to them from time to time. What made this threat both troubling and unusual was that it was emanating from a foreign government.

Intelligence officials are still trying to determine if the threat is valid and are re-assessing the additional security for Rubio on a day-by-day basis.

The threats against Rubio have not stopped him from continuing to criticize the Venezuelan government. Rubio has emerged as the leading voice of US opposition to Maduro and his government. While other members of the United States government – UN Ambassador Nikki Haley, Treasury Secretary Steve Mnuchin, and National Security Advisor H.R. McMaster – have all been critical of Venezuela, Rubio has become Maduro’s fiercest critic.

Earlier this year, Rubio brought the wife of a jailed Venezuelan opposition leader to the White House to meet with President Trump and Vice President Pence. A picture taken in the Oval Office of Trump, Pence, Rubio and Lilian Tintori, wife of opposition leader Leopoldo Lopez, was tweeted by Rubio and re-tweeted by the President.

Rubio’s attacks have grown even sharper following last month’s election that many believe eviscerated the country’s constitution and will essentially allow Maduro to exert control over every aspect of the government. The United States labelled the vote a “sham election,” and other countries have also refused to recognize the results including Canada, Mexico, Argentina and Brazil.

Following the Venezuelan election, Rubio pushed for the Trump Administration to enact sanctions against Maduro, freezing whatever assets they had in the United States. In making the announcement US officials said the sanction placed Maduro in an “exclusive club” of dictators that included Syrian President Bashar al-Assad, North Korean leader Kim Jong UN and Zimbabwean President Robert Mugabe.

Rubio also took the extraordinary step of addressing the people of Venezuela through one of the country’s independent TV stations. “If the Maduro regime is so confident in the support of its people, then why not schedule the free and fair election called for in your constitution,” Rubio asked. “Why not submit yourselves to the people in an election that recognizes the principles of one person and one vote?”

He added: “For Nicholas Maduro, who I am sure is watching, the current path you are on will not end well for you.”

And in an interview with the Miami Herald, Rubio said: “Politically speaking, if I were Nicolas Maduro, I would sleep with one eye open every night.”

President Trump last week raised the stakes further by noting the United States was willing to consider military options against Venezuela. It is not known if President Trump was aware of the threat against Rubio at the time he made that statement or if it played into his unexpected comments.

Over the past few weeks, Rubio and Cabello have been trading barbs on Twitter. Rubio now regularly refers to him as “Diosdado ‘Pablo Escobar’ Cabello” and Cabello in turn refers to Rubio as “Narco Rubio,” a possible reference to the 1987 arrest of Rubio’s brother-in-law for distributing cocaine. Rubio was 16 at the time and has denied knowing anything about it.

The Department of Homeland Security, the Capitol Police, the Senate Sergeant-at-Arms, and local police agencies in South Florida have all been alerted to the threat.

The Capitol Police, which is the agency primarily responsible for providing security to members of Congress, declined to comment. “We do not comment on how we carry out our protective responsibilities for Congress,” a spokeswoman for the agency said.

Rubio’s office declined to comment.

One local law enforcement official familiar with the threat against Rubio said what makes the situation even more complicated is the large Venezuelan population here. There are more than 100,000 Venezuelans living in Florida, with the vast majority in South Florida. Many of those living here oppose Maduro. In order to keep track of his critics, law enforcement officials believe there are Venezuelans who were sent here to spy on opposition leaders in South Florida.

“This is right out of the Cuban playbook,” said the local official.

For decades the Cuban government has sent agents to Miami to monitor anti-Castro groups.