Japan lodged a formal protest with China after a Chinese warship aimed a radar used to guide missiles at a Japanese ship, Japan's defense minister said today, raising the stakes in an ongoing spat over disputed islands in the East China Sea.

The incident near the Senkaku or Diaoyu islands last week was the first involving naval ships from two countries and followed an incident earlier in January where a Chinese warship directed its radar towards a Japanese military helicopter, Itsunori Onodera said.

"One misstep could have led to a very dangerous situation," Onodera told reporters.

Japan and China have been locked in an ongoing dispute over a group of uninhabited islands claimed by both countries in the East China Sea. Sino-Japanese tensions escalated last September after Japan purchased some of the islands, angering Beijing and triggering widespread anti-Japanese protests.

The countries have been involved in a near daily cat and mouse boat chase since then in disputed waters, but the spat has escalated in recent months, raising concerns of an unintended military conflict. Tokyo scrambled fighter jets in December and January after Chinese planes violated what Japan considers its airspace.

China did not fire in either incident in the high-seas stare down, but the move is seen as a direct threat against Japan, and sure to further inflame Sino-Japanese tensions.

Onodera said the Japanese government had lodged a protest with China through diplomatic channels in Tokyo and Beijing, to avoid similar incidents in the future.

"We will place strict demands on China and ask that they exercise self-restraint against engaging in such dangerous acts," he said.