The Biden administration believes that a Chinese hacking operation which breached US government email systems, including the State Department, gave the Chinese government insights about US thinking heading into Secretary of State Antony Blinken's trip to Beijing in June, according to two US officials.

The hack -- which Microsoft said was launched in mid-May -- was discovered by the State Department right around the time of Blinken's visit to Beijing, officials said. But it was not immediately clear that China was behind it and it was not widely known about within the department, they said.

Microsoft Executive Vice President Charlie Bell said that the company began investigating after customer reports came into the company on June 16 -- the same day that Blinken departed the US for his trip to Beijing.

The amount that China was able to learn from the hack was limited because it only breached an unclassified system, and US officials generally operate with the assumption that anything on the unclassified systems can be hacked. Still, it provided the Chinese government with additional knowledge from the private discussions of US officials heading into Blinken's visit.

Another target of the hack, Commerce Secretary Gina Raimondo is also expected to soon visit China.

The State Department did not immediately respond to a request for comment.

On Wednesday State Department Spokesperson Matt Miller said that the department had "detected anomalous activity" in June. He said the department immediately took steps to secure the system and notify Microsoft of the event.

"As a matter of cyber security policy, we do not discuss the details of our response. The incident remains under investigation, and we continuously monitor our networks and update our security procedures," Miller added.

This story is breaking and will be updated.