When questioned about a Washington Post report on Chinese hacking into its defense cyber networks, the top government spokeswoman stated on Tuesday that Japan was unable to determine whether any security information had been compromised.

According to senior sources quoted in the Washington Post on Monday, Chinese military hackers got access to a secure defense network in Japan starting in 2020 and obtained details about the military capabilities, strategies, and assessments of inadequacies of the U.S. ally.

The chiefs of the U.S. National Security Agency traveled to Tokyo after learning about the incident to tell the Japanese defense minister, who requested that the Americans notify the prime minister directly, according to the newspaper article.

Hirokazu Matsuno, the chief cabinet secretary of Japan, stated that the United States and Japan have always maintained close communication on a variety of levels during a routine news briefing on Tuesday.

“Due to the nature of the matter, I am unable to provide further details of the communication, but we haven’t confirmed the fact that security information has been leaked due to cyber attacks,” he said.

Beijing didn’t immediately respond with a response.

Matsuno added that Japan will keep working to make its network strong and safe and that cyber security is the cornerstone of the Japan-U.S. relationship.

According to authorities quoted by the Washington Post, Japan’s poor progress in enhancing its cyber network may prevent broader intelligence cooperation between the Pentagon and the Japanese Defense Ministry.