Beijing and Tokyo were at loggerheads Tuesday over accusations Japanese warplanes locked their fire control radar onto Chinese aircraft, as state-run Chinese media said the country needed to be ready for "military confrontation" elsewhere.
Beijing has long been embroiled in fierce territorial disputes with Tokyo over Japanese-controlled islands in the East China Sea, and with a host of littoral states over the South China Sea, which it claims almost in its entirety.
Chinese vessels and planes regularly enter waters and airspace near the East China Sea islands, called Senkaku in Japan and Diaoyu in China.
China's defence ministry late Monday accused Japanese fighter jets of using their fire control radar to lock onto two Chinese aircraft on "routine patrol" in the Air Defence Identification Zone (ADIZ) it declared unilaterally in 2013.
The aggressive move generally means an attacker is ready to fire weapons at a target.
Japan's deputy chief cabinet secretary Koichi Hagiuda denied the accusation Tuesday, telling reporters that Tokyo's Self-Defence Forces had scrambled F15 jets to monitor Chinese aircraft.
"There are no facts showing that we took provocative action against Chinese military planes," he said.
In 2013, Tokyo demanded Beijing apologise when it said a Chinese frigate had locked its fire-control radar onto a Japanese destroyer in international waters.
The row over the islands has seen relations between the world's second- and third-largest economies plunge in recent years, before recovering slightly, although they remain poor.
Beijing is also involved in a separate set of territorial disputes with other littoral neighbours over its extensive claims in the strategic and resource-rich South China Sea.
It has rapidly built up reefs and outcrops into artificial islands with facilities capable of military use.
The issue has raised tensions in the region and with the United States, which has key defence treaties with Japan and other allies in the area.
On Tuesday, China began a week of naval exercises in waters around the Paracel Islands, in the northern part of the sea.
They came a week before a United Nations-backed tribunal in The Hague rules on a case brought by the Philippines challenging China's position.
Beijing has boycotted the hearings and is engaged in a major diplomatic and publicity drive to try to delegitimise the process.
- Bitter pill of humiliation' -
In an editorial Tuesday, the Global Times -- a newspaper owned by the People's Daily group that often takes a nationalistic tone -- said China should accelerate the build-up of its defence capabilities and "must be prepared for any military confrontation".
"Even though China cannot keep up with the US militarily in the short-term, it should be able to let the US pay a cost it cannot stand if it intervenes in the South China Sea dispute by force," it added.
Beijing also accuses Tokyo of interfering in the South China Sea, where it is not a claimant but has strengthened ties with some of the Asian giant's rivals, including the Philippines.
China bases its maritime claims on a vaguely defined "nine dash line" dating back to maps it produced in the 1940s, and has been asserting them more aggressively in recent years.
Manila lodged its suit against Beijing at the Permanent Court of Arbitration (PCA) in early 2013, saying that after 17 years of negotiations it had exhausted all political and diplomatic avenues to settle the dispute.
The tribunal will issue its ruling on July 12, though China has consistently rejected its right to hear the case and has taken no part in the proceedings.
At a regular briefing on Tuesday, Chinese ministry of foreign affairs spokesman Hong Lei reiterated that Beijing rejected all third-party resolutions of the dispute.
The hearing would "in no way help peace and stability" in the region, he said, adding: "We will not accept any settlement imposed on us."
The arbitration case had been orchestrated by the Philippines and the US to portray China as "an outcast from a rules-based international community", said an editorial in the China Daily.
The newspaper, which is published by the government, added: "It is naive to expect China to swallow the bitter pill of humiliation".