Cuba’s communist-run government is facing its biggest test since the collapse of the Soviet Union.

U.S. President Donald Trump has ratcheted up the pressure on the Caribbean island since the Jan. 3, military operation to seize Venezuelan President Nicolás Maduro, a long-time ally of Cuba’s government. Cuba said 32 of its citizens were killed in the attack.

Trump has since effectively cut Cuba off from Venezuelan oil, called its government “an unusual and extraordinary threat” and pledged to impose tariffs on any country that supplies it with oil.

Cuban President Miguel Díaz-Canel condemned the move and said: “Surrender is not an option.” He’s since said the government is prepared to hold talks with Washington, albeit “without pressure or preconditions.”

The country has warned that international airlines would no longer be able refuel in the country due to fuel shortages. Gripped by a worsening economic crisis, Cuba’s government recently adopted rationing measures to protect essential services and ration fuel supplies for key sectors.

The plan reportedly includes restrictions on fuel sales, the closure of some tourist establishments, shortening school days and a shorter working week at state-owned companies to four days, from Monday to Thursday.

“The current situation in Cuba is as serious as it has been since the 1990s, when Cuba suddenly had to survive without the support of the Eastern Bloc,” Par Kumaraswami, professor of Latin American Studies at the U.K.’s University of Nottingham, told CNBC by email.

Trump’s tariff threats have created a deterrent for many nations, Kumaraswami said.

Mexico has sent humanitarian aid but suspended oil shipments, as it sought to preserve its relationship with Havana while avoiding Trump’s tariffs.

Kumaraswami said there was “of course frustration with the difficulties of daily life,” but that “many Cubans are resolved to resist threats to their national sovereignty and a new wave of patriotism has emerged.”

Air Canada subsequently has canceled all flights to Cuba amid the fuel shortage, though the airline said Monday that it would bring some 3,000 customers already in the country home over the coming days.

Tourism is a significant source of revenue for Cuba’s cash-strapped government and the country is a popular winter vacation destination for Canadian tourists.

Unlike in previous crises, Cuba’s regime lacks foreign partners that can step in to help, according to Robert Munks, head of Americas research at risk intelligence company Verisk Maplecroft.

“Raising the stakes, the US has also limited Cuba’s access to hard currency and pressured Nicaragua to end visa-free travel for Cubans,” Munks told CNBC by email.

The government’s pledge to increase the use of limited renewable energy sources is likely “too little, too late,” Munks said. He added that outbreaks of civil unrest were possible, given that the island’s domestic energy production is far short of what it needs to keep the lights on.

“An accelerating collapse of basic services will put the regime under extreme pressure to find a negotiated solution,” Munks said.

He added that “the odds are shortening” on Díaz-Canel being forced from power in the months ahead in a Maduro-style managed transition, but Munks said it was more likely that “the regime will try to muddle through” until the U.S. midterm elections in November.

Cuba’s dwindling oil supplies prompted the United Nations to warn of a possible humanitarian “collapse” last week.

“The Secretary-General is extremely concerned about the humanitarian situation in Cuba, which will worsen, and if not collapse, if its oil needs go unmet,” said UN spokesperson Stéphane Dujarric.

A spokesperson for China’s foreign ministry said Tuesday that Beijing “stands firmly against the inhumane actions that deprive the Cuban people of their right to subsistence and development.” They added that China would, “as always,” seek to provide assistance to Cuba.

Russia, meanwhile, has described Havana’s fuel situation as “truly critical” and said U.S. attempts to further pressure the country were causing numerous problems.

“The Cuban government is not going to submit,” Yaffe said. “The fact is, [the U.S. is] going to keep squeezing and the Cubans are going to keep resisting and there’s going to be a lot of unnecessary suffering.”

She added: “I’m a historian and it’s very vainglorious for historians to try and predict the future but we can look at trends — and I can guarantee you that we were here before in the early 1990s where nobody thought Cuba would pull together and pull through — and they did.”

The Cuban government said international airlines can no longer refuel there due to fuel shortages after U.S. President Donald Trump threatened tariffs on any country that supplies the communist country with oil.

The island nation’s leadership said Sunday that Cuba will run out of aviation fuel from Monday, likely disrupting operations airlines operating there, according to EFE news agency, citing two sources.

The kerosene shortage is expected to persist for the next month, with all of Cuba’s international airports affected.

Cuba’s Foreign Ministry and the Cuban Embassy in London did not immediately respond to a CNBC request for comment.

Trump, in an executive order issued at the end of January, said the Cuban government constituted “an unusual and extraordinary threat,” which required a national emergency declaration.

The U.S. president said that Cuba’s ties to countries including China, Russia and Iran, human rights violations and communist leadership destabilize the region “through migration and violence.”

As part of the announcement, Trump said U.S. tariffs may target countries that provides any oil to Cuba, whether directly or indirectly.

The Trump administration has sought to tighten the U.S. chokehold on Cuba since Jan. 3, when it conducted an audacious military operation to depose Venezuelan President Nicolás Maduro, a long-time ally of Cuba’s government.

The plan reportedly includes restrictions on fuel sales, the closure of some tourist establishments, shortening school days, and a reduction of the working week in state-owned companies to four days, from Monday to Thursday.

Russia, which holds friendly ties with Cuba, said Monday that Havana’s fuel situation was “truly critical” and that U.S. attempts to further pressure the country were causing numerous problems.

“The situation in Cuba is truly critical. We know this. We are in intensive contact with our Cuban friends through diplomatic and other channels. Indeed, let’s say the U.S.’s stranglehold is causing many difficulties for the country,” Kremlin Spokesperson Dmitry Peskov told reporters on Monday, according to state news outlet RIA Novosti.

Cuba’s Foreign Minister Bruno Rodríguez Parrilla previously said the country’s leadership condemned Washington’s tariff threats in the “strongest possible terms.”

In a statement posted on Jan. 30, Parrilla also accused the U.S. government of resorting to “blackmail and coercion in an attempt to make other countries to join its universally condemned blockade policy against Cuba.”

Mexican President Claudia Sheinbaum said last week that her government would aim to send humanitarian aid to Cuba from Monday, adding that the country is working to find a diplomatic solution to resume oil shipments to the Caribbean island.

Mexico had paused shipments of crude and refined products to Cuba amid pressure from the Trump administration.