Japan increased its surveillance in the East China Sea on Wednesday, the one-year anniversary of its purchase of a group of islands there that are also claimed by China.
Ties between Asia's two largest economies reached their lowest point in years after Japan bought some of the islands from their private Japanese landowner 12 months ago.
China refused to recognize the sale. It responded by sending increased sea and air patrols to the islands in what is seen as an attempt to assert Beijing's claim to the strategic area.
Japanese Deputy Cabinet Secretary Katsunobu Kato said Wednesday that Tokyo will stand firm in its position on the islands, but hopes for a diplomatic resolution to the tensions.
"We will take all measures necessary to protect our sovereignty, territory and airspace as necessary while also looking to react in a calm manner," her said. "We do not want to escalate the situation from the Japanese side. We look to continue to talk with the Chinese side and improve the situation."
A government spokesman on Tuesday said Japan has not ruled out deploying officials to the uninhabited island chain, a comment that drew a sharp rebuke by Beijing.
China's foreign ministry said Beijing was "gravely concerned" by the remarks and warned that Japan will have to "accept the consequences" if it "recklessly makes provocative moves."
Japanese Prime Minister Shinzo Abe has called for high-level talks to resolve the dispute. But China has rejected his offer as insincere, saying Tokyo must first make concessions to reduce tensions.
At sea, meanwhile, government patrols ships and airplanes from both countries continued to engage in minor standoffs and confrontations, raising fears of a military clash.
On Tuesday, Japan formally complained to Beijing over the presence of eight Chinese government ships in the area. The Japanese coastguard says the flotilla was the biggest of its kind since April.
On Monday, Japan scrambled fighter jets in the East China Sea after it spotted what it said was an unmanned aircraft flying toward Japan.
The islands, known as Senkaku in Japan and Diaoyu in China, are uninhabited, but surrounded by rich fishing ground and potential energy deposits.
Japan annexed the islets in the late 19th century. China claimed sovereignty over the archipelago in 1971, saying ancient maps show it has been Chinese territory for centuries.