One of Venezuela’s most powerful leaders may have put out an order to kill U.S. Sen. Marco Rubio, R-Fla., a fervent critic of the South American country’s government, according to intelligence obtained by the U.S. last month.

Though federal authorities couldn’t be sure at the time if the uncorroborated threat was real, they took it seriously enough that Rubio has been guarded by a security detail for several weeks in both Washington and Miami.

Diosdado Cabello, the influential former military chief and lawmaker from the ruling socialist party who has publicly feuded with Rubio, was believed to have issued the order.

At a July 19 Senate hearing, the same day he was first spotted with more security, Rubio repeated his line that Cabello — who has long been suspected by U.S. authorities of drug trafficking — is “the Pablo Escobar of Venezuela.” A week ago on Twitter, Cabello called the senator “Narco Rubio.”

The death threat was outlined in a memo to several law enforcement agencies last month by the Department of Homeland Security. The memo, designated “law enforcement sensitive” but not classified, was obtained by the Miami Herald.

The memo revealed an “order to have Senator Rubio assassinated,” though it also warned that “no specific information regarding an assassination plot against Senator Rubio has been garnered thus far” and that the U.S. had not been able to verify the threat. That Cabello has been a Rubio critic in Venezuelan media was also noted, a sign that federal authorities are well aware of the political bluster complicating the situation.

According to the memo, Cabello might have gone as far as to contact “unspecified Mexican nationals” in connection with his plan to harm Rubio.

Rubio has led the push for a robust U.S. response against Venezuelan President Nicolas Maduro’s government before and after a disputed July 30 vote that elected a new legislative body whose powers supersede all other government branches, including the opposition-held parliament.