Washington, Jun 9 (IANS): Chinese government hackers have compromised the computers of a US Navy contractor, stealing massive amounts of highly sensitive data related to undersea warfare, including secret plans to develop a supersonic anti-ship missile.

The Navy is leading the investigation into the breach--that occurred in January and February--with the assistance of the FBI, US officials said on Friday.

The hackers targeted the contractor who works for the Naval Undersea Warfare Centre -- a military organisation headquartered in Rhode Island's Newport city -- that conducts research and development for submarines and underwater weaponry, The Washington Post reported.

The officials did not identify the contractor.

The hackers took 614 gigabytes of material related to a closely held project known as Sea Dragon, as well as signals and sensor data, submarine radio room information relating to cryptographic systems, and the Navy submarine development unit's electronic warfare library.

The data stolen was of a highly sensitive nature despite being housed on the contractor's unclassified network.

The officials said the material, when aggregated, could be considered classified, a fact that raises concerns about the Navy's ability to oversee contractors tasked with developing ­cutting-edge weapons.

Navy spokesman Commander Bill Speaks said: "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."

Speaks added that "it would be inappropriate to discuss further details at this time."

On Friday, the Pentagon Inspector General's Office said Defence Secretary Jim Mattis had asked it to review the contractor cybersecurity issues.

The breach is part of China's long-running effort to blunt the US advantage in military technology and become the preeminent power in East Asia.

The news comes as President Donald Trump's administration is seeking to secure Beijing's support in persuading North Korea to give up nuclear weapons, even as tensions persist between the US and China over trade and defence matters.