The Defense Ministry on Friday criticized Japanese fighter jets that disturbed routine patrols by Chinese aircraft over the East China Sea amid lingering tensions over the Diaoyu Islands.

Tokyo also ramped up its hardline stance as Japanese Prime Minister Shinzo Abe said on Friday there was "no room for negotiation" on the row.

Analysts said Tokyo is now keen to test Beijing's bottom line by flaring up military confrontation, and to seek more bargaining chips for future talks.

China's Ministry of National Defense said on Friday China sent two J-10 fighters to the East China Sea after a Y-8 transport aircraft was closely followed by two Japanese F-15 fighters when patrolling the East China Sea on Thursday.

Japan's military aircraft have been "increasingly" active in closely scouting Chinese aircraft and have expanded their activity zone, which the ministry said is the root reason for bilateral security disputes on the sea and in the sky.

Cao Weidong, a researcher at the Naval Military Studies Research Institute, said Tokyo's decision to take the initiative to dispatch F-15 fighter jets is a risky move that is "increasing the possibility of a drastic escalation.

"Sending military aircraft to a disputed area is viewed as a provocation, and Beijing was forced to respond for defensive purposes," Cao said.

Bilateral relations, including trade, have suffered since Tokyo's illegal "purchase" of China's Diaoyu Islands in September and masses of Chinese took to the streets to protest the move.

Tokyo has ramped up approaches to intimidate regular patrols around the islands by Chinese Marine Surveillance ships.

Tension over the East China Sea was fueled in December when eight Japanese F-15 fight jets attempted to hold down a Chinese aircraft, which was on a routine patrol.

Japanese Prime Minister Abe on Friday claimed that China has deliberately targeted Japanese companies as part of a strategy to confront Japan over the countries' territorial row.

Gao Hong, an expert on Japanese studies from the Institute of Japanese Studies at the Chinese Academy of Social Sciences, said Beijing has not resorted to economic sanctions, but Tokyo is eager to "find a scapegoat" when explaining to Japanese entrepreneurs who have suffered a lot in China.

"Japan's provocation gave rise to the Chinese public's spontaneous boycott, and public opinion deserves respect," Gao said.

Gao said Abe's tough words of "no room" for territorial negotiation are to test Beijing's bottom line.

"And his hostility against China is intended to polish his image and gain more domestic support," Gao said.

Takehiko Yamamoto, a professor at Waseda University in Japan, told AFP that "perhaps the undercurrent of the message was that China is a necessary partner for Japan's growth strategy to climb out of deflation".

In addition to his vow of no change in his position to resolutely "protect the water and territory", Abe also reiterated on Friday that he wants to improve Japan-China ties on the basis of "strategic mutually beneficial relations".

Abe had posed as a hardliner on disputes before his landslide election victory in December, yet after retaking the premiership, he also mentioned "strategic mutually beneficial relations" several times.

Foreign Ministry spokesman Hong Lei said Japan has pushed bilateral relations into a difficult situation, and it should "show sincerity, face up to reality" and work with China for a proper resolution.