Japan has recorded a protest with China on Sunday after Chinese fighter jets directed fire-control radar at Japanese fighter jets near Japan's Okinawa islands.

Japan's Defense Minister, Shinjiro Koizumi, denounced the Chinese military's moves as "dangerous".

"These radar illuminations went beyond what is necessary for the safe flight of aircraft," he said.

"The occurrence of such an incident is extremely regrettable," the minister added. "We have lodged a strong protest with the Chinese side and demanded strict preventive measures."

A radar lock is considered as one of the most threatening acts by a military aircraft as it signals a potential attack, forcing the targeted plane to take evasive action.

Fighter aircrafts can also use radars for search.

What do we know about the incident?

Japan's Defense Ministry said that Chinese J-15 military jet "intermittently" targeted its radar at Japanese F-15s in two incidents on Saturday — for about three minutes in the afternoon and 30 minutes in the evening.

It was not immediately known if the radar lock was from the same Chinese J-15 on both occasions.

Japan said the Chinese J-15 aircraft involved in the two radar lock incidents was launched from China's Liaoning aircraft carrier.

Liaoning was maneuvering between the main island of Okinawa and nearby Miyako island on Saturday, as it carried out aircraft takeoff and landing drills in the Pacific.

The radar lock was detected by different Japanese fighters that had scrambled against a possible airspace violation by China, the ministry said.

The Japanese airspace was not breached.

"China's intentions are unclear, but if it is to locate (aircraft), there is no need to do that intermittently," Japan's Kyodo news agency cited a defense ministry official as saying at a press conference.

According to Japanese media, Japan's Sunday statement marked the first time that the defense ministry in Tokyo publicly disclosed a fire-control radar lock  incident by Chinese military jets against Japanese aircraft.

In 2013, Japan said that a Chinese warship locked its radar on a Japanese destroyer in the East China Sea.

China-Japan ties worsen over Taiwan

The radar-lock incident is the latest row between the two Asian nations whose ties have soured in recent weeks over Taiwan, the self-governing island that China claims as its own territory.

Beijing has been irked after Japanese Prime Minister Sanae Takaichi said in November that her country's military could get involved if China were to take action against Taiwan.

Edited by: Dmytro Hubenko