President Nicolás Maduro holds up a copy of Venezuela's constitution as he speaks during a national TV broadcast in Caracas. (Miraflores Palace via Reuters)

HAVANA — President Obama's attempt to mend relations with Cuba while simultaneously turning the screws on Venezuela, Havana's closest ally, is making for some fascinating triangular diplomacy.

Late Monday night, after Venezuelan President Nicolás Maduro gave a speech blasting new U.S. sanctions on his administration as an attempt to overthrow him, the Cuban government affirmed its "unconditional support" for Maduro.

Then 88-year-old Fidel Castro chimed in for good measure.

"Dear Nicolás Maduro," Castro wrote in a brief message published by Cuban state media that was almost tight enough for a Twitter posting. "I congratulate you for your brilliant and brave speech in the face of the brutal plans by the United States government."

"Your words will go down in history as proof that humanity can and will know the truth," he wrote.

It was telling that the message of support came from the elder Castro, and not his brother, President Raúl Castro.

Raúl Castro, 83, is the one who has worked out the diplomatic reconciliation with Obama and will meet with the U.S. president next month at the Summit of the Americas in Panama.

His older brother has offered tepid support for the U.S. thaw he's charted, but nothing that would qualify as enthusiasm. And while Raúl Castro also regularly pledges to support the Venezuelan president, he does not have the same close personal relationship with Maduro, who, like his predecessor Hugo Chávez, embraces Fidel Castro as a political mentor.

Venezuela remains Cuba's top trading partner, and as Caracas replaces Havana as the principal U.S. adversary in the region, the Castro government is caught in the middle. Havana can't afford to hitch its fortunes to the cash-squeezed Venezuelan government and its wobbly president, who lacks the political acumen of Chávez.

In the coming weeks and at the Panama summit, Cuba is likely to continue voicing support for Venezuela while quietly working out its new relationship with the United States. It'll be a delicate balancing act, especially as critics of Obama's opening to Cuba blame rights abuses in Venezuela on a repressive security strategy that they say is being dictated from Havana.

Since the White House announced the sanctions on Monday, Venezuela, Cuba and many in the region have reacted less to those measures than to language in the executive order characterizing the Maduro government as a threat to U.S. national security.

U.S. officials say it's boilerplate language used whenever such sanctions are imposed, but Venezuela's government and its backers have seized on the "security threat" element to claim that it's some sort of prelude to an American attack.

After defiantly bestowing promotions on one of the security officials named on the U.S. sanctions list, Maduro said Monday night that he'll seek emergency decree powers "to fight imperialism."

Venezuela's opposition leaders say it's a naked power grab to further stifle dissent.

Asked to respond to Maduro’s charge of U.S. plotting, State Department spokesman Jen Psaki said Tuesday that the administration’s “intention is not promoting unrest in Venezuela … or undermining its government.” Instead, she said, “it’s about making clear that we don’t accept human rights abusers or corrupt officials.”

The “goal of sanctions,” Psaki said, “is to persuade the government to change their behavior.”

She cautioned against focusing on the “national emergency” and security threat language in Obama’s executive order, noting that it is standard in such orders. “It’s important for everybody to understand that this is how we describe the process of naming sanctions,” Psaki said. Monday’s Venezuela order was “consistent with how we announce and how we describe putting sanctions and putting these executive orders in place.”

Meanwhile, tensions in Venezuela were further inflamed Tuesday by a comment made on a pro-government talk show by Roy Chaderton, the Maduro government's ambassador to the Organization of American States (OAS), which is organizing the Panama summit.

In response, apparently, to a question about how the government would handle new security threats, Chaderton told viewers that when snipers shoot opposition demonstrators in the head, a different sound is emitted. "Because their cranial cavity is empty," he said dryly, presumably trying to make a joke.

Chaderton's comment appeared with the Twitter hashtag "ObamaYankeeGoHome."

Anti-government street demonstrations in the country last year left 43 dead, and some of the victims were shot by Venezuelan security forces, who have since been granted additional latitude to use lethal force against protesters.

Karen DeYoung contributed to this report.