Japan's Prime Minister Shinzo Abe (L) looks at China's President Xi Jinping during a welcoming ceremony of the Asia Pacific Economic Cooperation (APEC) forum, inside the International Convention Center at Yanqi Lake, in Beijing, November 11, 2014. Reuters/Kim Kyung-Hoon Chinese state media has launched a volley against a Japanese news outlet for publishing detailed photographs of the PLA aircraft carrier being assembled in a port in Dalian, saying the move posed a grave threat to national security.

In a front-page commentary, the China National Defence Daily said the high-resolution images, which showed the vessel covered with scaffolding amid towering cranes, were a “wake-up call” for the country to better protect military secrets.

Beijing has classified the carrier project and its existence was only confirmed last year.

Kyodo News published the photos two weeks ago, saying they were obtained from an undisclosed source and taken in late December. The carrier is China’s first domestically made one and will join the retrofitted Liaoning. Work was almost completed, Kyodo said.

Neither Kyodo nor the Chinese defence ministry immediately responded to requests for comment.

Little is know about the carrier project, other than state-owned China Shipbuilding Industry is carrying it out. Kyodo did not identify where exactly the photos were taken or whether the shipyard is a military or civilian facility. Chinese law prohibits taking photos of military areas.

Four Japanese citizens were arrested last year on suspicion of spying, and Kyodo last Thursday cited a Japanese government source as saying one of the accused had gone on trial in Beijing.

In its commentary, the National Defence Daily said advances in technology, such as more sophisticated cameras and the emergence of drones, posed challenges for the safeguarders of the nation’s secrets.

A live-fire drill using an aircraft carrier is seen carried out in the Bohai sea, China, December 11, 2016. Reuters

“Nowadays, our security environment is experiencing profound and complicated changes,” it said. “Painful lessons in history” had made clear that preventing spying and protecting national security interests were critical. “We must not relax,” it said.

It suggested local governments and military authorities step up counter-espionage efforts, including encouraging people to act as “intelligence patrolmen”, and for better monitoring of the nation’s military enthusiasts who share information online.

China marked its first National Security Education Day in April, circulating posters that warned young women government workers to be cautious about “honeytraps”, where attractive foreigners working for overseas interests entice them into revealing any valuable information they know.

Kyodo is not the first to publish images of the aircraft carrier – IHS Jane’s Defence Weekly published satellite images in October last year, suggesting construction had begun.

Song Zongping, a commentator on military affairs for Phoenix Satellite Television in Hong Kong, said that by highlighting the Kyodo report, Beijing was trying to send a message to Japan about treading carefully. “By exposing the high-resolution photo incident, it is warning Japan not to do anything threatening China’s national security,” Song said.

Highlighting the incident also served to remind the public to resist falling prey to honeytraps.