The White House denied a report Thursday that China is planning to set up a surveillance base just off US shores in Cuba.
The Wall Street Journal reported that Beijing and Havana have entered into a secret agreement for a Chinese electronic eavesdropping facility on the Caribbean island that could monitor communications across the southeastern United States.
The region includes the US Southern and Central Command headquarters, both in Florida.
China will pay Cuba "several billion dollars" to be able to construct the facility, the Journal said, citing unnamed US officials.
White House national security spokesman John Kirby denied the story.
"I've seen that press report. It's not accurate," Kirby told MSNBC.
"What I can tell you is that we have been concerned since day one of this administration about China's influence activities around the world, certainly in this hemisphere and in this region," he said.
"We are watching this very closely," he added.
Pentagon spokesman Pat Ryder also called the Journal report inaccurate.
"We are not aware of China and Cuba developing any type of spy station," Ryder said, adding: "The relationship that those two countries share is something that we continuously monitor."
But Democratic Senator Mark Warner and Republican Marco Rubio, who head the Senate Intelligence Committee and are usually briefed on important security matters, said in a statement that they were "deeply disturbed" by the Journal report.
"The United States must respond to China's ongoing and brazen attacks on our nation's security," they said.
"We must be clear that it would be unacceptable for China to establish an intelligence facility within 100 miles of Florida and the United States."
The Journal report came amid strained relations between Washington and Beijing over a range of issues that include US support for self-ruled Taiwan, which China says it is determined to reunite with the mainland.
Chinese leader Xi Jinping has pushed a rapid expansion of the country's security presence around the world, aiming to match the broad presence of the US military on all the continents.
A base in Cuba, which lies 90 miles (150 kilometers) off the southern tip of Florida, would present the most direct challenge yet to the continental United States.
The Soviet Union had electronic spying facilities in communist Cuba to monitor the United States.
But in 1962 when Moscow moved to base nuclear missiles on Cuba, the US declared a quarantine of the island in a crisis that threatened to bring the two superpowers to war, until Moscow backed down.
Washington then removed its nuclear-capable missiles from Turkey, which the Soviets viewed as a threat to them.
China sent what the US called a high-altitude surveillance balloon across the United States earlier this year. It floated from west to east above sensitive military installations before it was shot down just off the east coast by a US fighter jet.