Japan's prime minister called China's radar-lock on a Japanese navy ship a "dangerous act" on Wednesday.
A day after Japan claimed a Chinese ship directed a weapons-related radar system at a Japanese vessel on Jan. 30, Shinzo Abe called for restraint in the island dispute in the East China Sea.
"I ask the Chinese side to return to the spirit of mutually beneficial, strategic relations and prevent the recurrence of an incident like this. I strongly ask them for restraints so that the situation will not escalate further," he said.
Asia's two largest economies both claim territorial sovereignty over uninhabited islands known as the Senkaku in Japan and the Diaoyu in China.
On Tuesday, Japanese Defense Minister Itsunori Onodera claimed that "something like fire-control radar" was directed at a Japan self-defense maritime escort ship.
US State Department spokeswoman Victoria Nuland commented on the alleged incident:
"With regard to the reports of this particular lock-on incident, actions such as this escalate tensions and increase the risk of an incident or a miscalculation, and they could undermine peace, stability and economic growth in this vital region," she said.
Beijing has yet to file a formal comment on the incident, according to the BBC.
The closest remark to a denial or a confirmation came from Chinese Foreign Ministry spokeswoman Hua Chunying.
"I have seen the reports but I don't understand the details of the situation," she told reporters, according to Reuters.