Hackers linked to the Chinese government broke into computers belonging to a Navy contractor and stole a trove of sensitive information about a U.S. Navy project and undersea warfare, The Washington Post is reporting.

The data pilfered from the contractor’s computer included plans on a U.S. project to build a supersonic anti-ship missile that can be mounted on American submarines by 2020, according to the Post, which cited an anonymous U.S. officials.

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The Chinese hackers targeted an unnamed contractor working for the Naval Undersea Warfare Center, a Navy research and development facility headquartered in Newport, R.I. They obtained 614 gigabytes of data on a secret project known as Sea Dragon, as well as signals and sensor data, documents on electronic warfare, and other information.

While the information was stored on the contractor’s unclassified network, it was described as “highly sensitive” in the Post report.

Security professionals have long observed Chinese spies conducting cyberattacks against U.S. defense contractors in order to spy on military capabilities.

The activity has persisted despite a landmark cyber pact between then-President Obama and Chinese President Xi Jinping in 2015 in which both parties agreed to stop supporting cyber-enabled intellectual property theft against businesses within one another’s borders.

The breaches in question occurred in January and February.

“There are measures in place that require companies to notify the government when a ‘cyber incident’ has occurred that has actual or potential adverse effects on their networks that contain controlled unclassified information,” Navy spokesman Cmdr. Bill Speaks was quoted as telling the Post.

Speaks further stated, “It would be inappropriate to discuss further details at this time.”

The development comes amid tense trade negotiations between the U.S. and China. Relations between both countries have also been strained over the South China Sea, where Beijing has made disputed territorial claims and deployed military systems.

Meanwhile, the Trump administration is seeking China's help in negotiating with North Korea over its nuclear weapons program. President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE is set to meet with North Korean leader Kim Jong Un in Singapore on June 12.