Chinese hackers broke into the computer networks of the U.S. government agency that keeps the personal information of all federal employees in March, the New York Times reported, citing senior U.S. officials.
The hackers appeared to be targeting files on tens of thousands of employees who have applied for top-secret security clearances, the newspaper said.
Asked about the report during annual high-level talks between the U.S. and China on Thursday, U.S. Secretary of State John Kerry said the "alleged incident" did not appear to have impacted sensitive information.
"What we have heard is that it relates to an attempted intrusion. It is still being investigated by U.S. authorities," he said. "At this point in time it does not appear to have compromised any sensitive material."
The hackers gained access to some of the databases of the Office of Personnel Management before federal authorities detected the threat and blocked them from the network, the newspaper said.
It was not yet clear how far the hackers penetrated the agency's systems, in which applicants for security clearances list their foreign contacts, previous jobs and personal information like past drug use.
Tensions are high between China and the United States.
The United States recently charged five Chinese military officers, accusing them of hacking into American companies to steal trade secrets. China showed its anger over the allegations by shutting down a bilateral working group on cyber security.
Bilateral talks between Beijing and Washington this week, called the Strategic and Economic Dialogue, focused on cyber-security as well as maritime disputes, the Chinese currency and an investment treaty.
(Reporting by Supriya Kurane in Bangalore, additional reporting by Lesley Wroughton in BEIJING; Editing by Paul Tait and Nick Macfie)