In an agreement to establish a spy base in Cuba Beijing and Havana have come to a conclusion, according to US officials quoted by the Wall Street Journal.

As noted in the article, China will allocate several billion dollars to Cuba for the construction of facilities. In addition, with the creation of a secret spy base, Beijing will be able to monitor American ships and communications in the southeastern United States.

The discovery alarmed the Biden administration due to Cuba’s proximity. Washington sees a Chinese base 100 miles away with advanced military and intelligence capabilities as an unprecedented threat. “While I can’t speak to this particular report, we are well aware – and have spoken many times – of China’s efforts to invest in infrastructure around the world, including in this hemisphere,” said John Kirby, spokesman for the National Security Advisor.

US officials declined to provide further details about where the base would be located or whether construction had begun.

News of new base comes amid Biden administration efforts improve relations with China after months of tension. Last month, President Biden sent CIA Director William Burns on a secret trip to Beijing, and National Security Adviser Jake Sullivan held talks with a senior Chinese official in Vienna. However, it is unknown if the above information was included in the discussions.

“The Cuba facility makes clear what China wants to do in America’s backyard,” said Craig Singleton, a fellow at the Defense of Democracies Foundation, a national security think tank. “The establishment of this facility marks a new phase of escalation in China’s broader defense strategy. This is a game changer,” Singleton said.

Analysts estimate that Beijing may justify the move by US military activity near China. For example, Washington militarily supports Taiwan, which the Chinese consider their province.

China’s only foreign military base is in Djibouti, in the Horn of Africa, and China has launched a global campaign to build ports in places like Cambodia and the United Arab Emirates.

The United States, for its part, maintains a military base in Guantanamo Bay in Cuba, which was established after the September 11, 2001 attacks to transport people with direct or indirect ties to Al-Qaeda and other terrorist organizations.

The Biden administration has sought to move closer to Havana by reversing some Trump-era policies, easing travel restrictions to and from Cuba, and restoring the family reunification program. The administration also expanded consular services to allow more Cubans to visit the US.

Cuba has been a thorn in the side of the US since it became a communist dictatorship after the 1959 revolution. The late dictator Fidel Castro, at the height of the Cuban missile crisis, sent a telegram to his Soviet colleague Nikita Khrushchev asking him to consider a nuclear attack on the US.

The US and Soviet Union were on the brink of nuclear war after the Soviets deployed nuclear-capable missiles in Cuba, prompting the US Navy to blockade the island. The Soviets retreated and removed the rockets. A few months later, the US quietly removed the medium-range ballistic missiles that the Soviets had complained about from Turkey.