The hope engendered three years ago by the announcement of the normalization of Cuba-US relations after almost six decades of enmity is now a distant memory, given US President Donald Trump's hostility toward Havana, and Russia has been taking full advantage of the

situation to reestablish its influence on the communist island.

Over the past six months the US-Cuban rapprochement had been moving slowly but now it seems to be under severe strain, the Cuban government warned this past week.

"The first adverse effects are already being felt," Josefina Vidal, the top official concerned with the US at the Cuban Foreign Ministry and the most visible face of the diplomatic thaw, said on Friday.

Although the number of US travelers to Cuba had shot up by almost 250 percent before beginning to decline, the bilateral dialogue on healthcare and the environment is paralyzed and top-level meetings in Havana have been moved to Washington.

Amid this disarray, Cuba's former Russian allies have begun to give unmistakable signals of renewed interest in the island, making vital moves for the Cuban economy such as sending a shipment of petroleum last May to alleviate the plunge in subsidized oil supplies from Venezuela.

Six months before then-US President Barack Obama and his Cuban counterpart, Raul Castro, announced the reestablishment of bilateral diplomatic ties, the Kremlin had forgiven 90 percent of Cuba's outstanding debt to Russia.

Just six months later, Castro met in Moscow with Russian President Vladimir Putin, and on Saturday the Cuban leader welcomed the head of Russia's biggest oil company, Rosneft chief Igor Sechin, who is considered to be Putin's right-hand man.

Russia, Cuba's fourth-largest trading partner, is participating in the modernization of the island's railway system and Russian tourism to Cuba had risen by 40 percent through September.

Moreover, Russia and Cuba in November 2016 signed several agreements in the military, transportation, electricity and medicine sectors.

New rules published by the US Treasury, Commerce and State Departments seeking to economically strangle the Cuban leadership have also created a climate of fear and uncertainty among US investors regarding the island.

"They are having an intimidating and dissuasive effect ... (and) they confirm the serious reversal in the two countries' links," Vidal said.

In the meantime, a number of US Embassy employees in Havana have been stricken with health problems after an apparent "sonic attack," the perpetrators of which are still unknown, and the Kremlin has confirmed its "unbreakable solidarity" with Cuba.