Four Chinese marine surveillance ships patrolled in waters around the territorial Diaoyu Islands on Monday and took law enforcement measures against Japanese vessels illegally sailing in the area, said the State Oceanic Administration.

The four Japanese vessels, carrying some 30 members of the Japan National Action Committee, a right-wing political group, departed from Ishigaki, Okinawa, Sunday evening and arrived in the waters near the Diaoyu Islands Monday morning for "fishing investigation" and to "declare sovereignty" before leaving in the afternoon, the Kyodo News reported.

This is the 15th time the group has entered the area, the last being on May 26, when it was driven out by three Chinese surveillance ships.

Kenji Yamada, a member of Japanese Prime Minister Shinzo Abe's Liberal Democratic Party (LDP) and a parliamentarian, was also aboard one of the boats, reported the AFP.

Chinese surveillance ships conducting regular patrols in the area responded to the Japanese patrol vessels arriving to guard the vessels and were "warned to leave the waters," according to the 11th Regional Coast Guard Headquarters in Naha, Okinawa.

Relations between China and Japan soured after the Japanese government "nationalized" part of the Diaoyu Islands in September, "purchasing" them from private hands in order to forestall their purchase by right-wing Tokyo governor Shintaro Ishihara.

"The civil action by the group this time could be a test of the government over the Diaoyu Islands as the ruling Liberal Democratic Party is focusing on the Senate election in July and doesn't bother to start new provocation," Wang Xiaopeng, a researcher of the Chinese Academy of Social Sciences (CASS), told the Global Times, adding that the group would have found a chance to land on the island if not stopped.

Chinese foreign ministry spokeswoman Hua Chunying on Monday urged Abe to take action to improve bilateral ties, adding that the current tensions were caused by the Japanese side, which has repeatedly taken provocative actions regarding the islands.

Abe said on Sunday he wishes to meet with China's leaders. "If there are issues to be solved, then it is the right diplomacy that we should meet and hold talks," Abe said, adding that any conditions for such meetings should not be set.

Yang Bojiang, a Japanese affairs expert with the CASS, said that chances for an official meeting between the top leaders in a short time are slim.

"It is better for the doer to undo what he has done," Hua said.

Chinese Foreign Minister Wang Yi and his Japanese counterpart Fumio Kishida passed by without even greeting during the Association of Southeast Asian Nations Foreign Ministers' Meeting in Brunei on Sunday, reported the Kyodo News. Hua said there is currently no plan for a meeting of the two.