Moscow, Russia - Russian Foreign Minister Sergei Lavrov said on Monday that economic and military "pressure" on ally Cuba was "unacceptable", after the US administration ratcheted up threats against the communist-run island nation.

US President Donald Trump has signed an executive order threatening additional tariffs on countries that sell oil to Cuba, which is suffering its worst economic crisis in decades.

Cuban President Miguel Diaz-Canel denounced the move, calling it an attempt to "suffocate" the country's economy.

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Lavrov reaffirmed "the unacceptability of economic and military pressure on Cuba, including the disruption of energy supplies to the island", according to a readout of his call with Cuban counterpart Bruno Rodriguez.

The Russian minister said the disruption of energy supplies to the island "threatens to seriously worsen the economic and humanitarian situation in the country".

He reiterated Moscow's "firm commitment to continue providing Cuba with the necessary political and material support".

AFP reporters saw Cubans queueing up in long lines at gas stations in Havana after the tariff announcement.

Tensions between Washington and Havana spiraled further after the US toppled Venezuelan President Nicolás Maduro, whose country was a crucial source for oil exports to Cuba.

The Caribbean island already struggles with repeated blackouts as it faces the most serious economic crisis since the 1991 collapse of the Soviet Union, its former principal benefactor.