Even as the meeting between Chinese leader Xi Jinping and U.S. Secretary of State Antony Blinken sought to defuse tensions between the two superpowers, China’s alleged activities in the Western Hemisphere threaten to derail such efforts.

When Blinken met President Xi and other Chinese senior officials on Monday, both sides led with diplomatic overtures aimed at improving strained bilateral relations.

For his part, Secretary Blinken told the Chinese leadership that the United States does not support Taiwanese independence. A senior Chinese official told Blinken, “We must reverse the downward spiral of China-U.S. relations, push for a return to a healthy and stable track, and work together to find a correct way for China and the United States to get along.”

But recent suspicious Chinese activity on the island nation of Cuba threatens to negate the cautious but friendly tones of the recent diplomatic summit.

U.S. officials acknowledged China has had a spy base in Cuba since 2019, The Wall Street Journal reported. More recently, China and Cuba have deepened military ties, negotiating for a joint training facility on the island’s northern coast, just 100 miles from the Florida coast.

According to WSJ, U.S. officials view China’s focus on Cuba as a deliberate counterbalance to the United States’ relationship with Taiwan. Mirroring Cuba’s geographic relationship to the U.S., Taiwan is an island situated roughly 100 miles from mainland China.

Blinken revealed on Tuesday that he discussed both Chinese spying and military involvement in Cuba with Beijing, expressing the U.S. government’s “deep concerns.”

“This is something we’re going to be monitoring very, very closely, and we’ve been very clear about that. And we will protect our homeland; we will protect our interests,” Blinken said.

The United States has long maintained a suspicious stance against China’s largest telecommunication companies like Huawei and ZTE for conspiring to steal trade secrets from American targets. In 2019, Huawei was added to a list of companies to which certain tech exports are restricted.

ZTE has also been the target of export restrictions since 2016. These measures were taken partly due to U.S. intelligence detecting the presence of Huawei and ZTE workers in Cuban facilities suspected of hosting spies during the Trump administration.

Huawei has called the accusations “groundless,” adding that it was “committed to full compliance with the applicable laws and regulations where we operate.”

Though Huawei denies spying for China, the Biden administration claims to be keeping an eye on Chinese spying operations from the Caribbean nation.

A White House official noted on Monday that China “will keep trying to enhance its presence in Cuba, and we will keep working to disrupt it,” per WSJ.