Beijing on Monday confirmed that diplomatic communication with Tokyo "remains" in the Diaoyu Islands dispute leading up to an ice-thawing trip to Beijing by key members of Japan's Cabinet.

Beijing urged Tokyo to handle the standoff calmly and with sincerity, while observers said it remains to be seen whether the Japanese ruling coalition's key members will bring constructive proposals to China during their visit.

China consistently advocates resolving territorial disputes through dialogue and consultation, while the country has both the "determination and capability" to protect its territorial sovereignty, Foreign Ministry spokesman Hong Lei said.

Hong made the remarks while criticizing Japanese Foreign Ministry's previous statements that accused China's growing presence on the Diaoyu Islands as "trying to change the status quo".

"Japan's so-called existence or control regarding the relevant sea area is illegal and invalid," Hong said.

China sent government aircraft from China Marine Surveillance for regular patrol over the Diaoyu Islands, yet "what Japan scrambled were fighter jets" trying to hold down Chinese airplanes, said Zhou Yongsheng, an expert on Japanese studies at China Foreign Affairs University.

Tensions flared over the islands in September after the Japanese government illegally "purchased" part of the Diaoyu Islands, and China Marine Surveillance has beefed up regular patrols of both vessels and aircraft around the Diaoyu Islands in the East China Sea.

To ease tensions, Japan should first cancel its erroneous "purchase" decision, and Tokyo should recognize the territorial row over the islands, said Dong Manyuan, vice-president of the China Institute of International Studies.

Zhou warned that it is impossible for Beijing to get the situation back to the time when the latest standoff was not triggered.

A Chinese marine surveillance fleet continued patrolling China's territorial waters around the Diaoyu Islands on Monday and found Japanese ships that entered China's territorial waters, according to the State Oceanic Administration.

The vessels, Haijian 137, Haijian 23 and Haijian 46, followed and monitored the Japanese ships, and demanded the Japanese ships' immediate departure from Chinese waters.

"China urges Japan to calmly handle the Diaoyu Islands issue and show sincerity in working with China to properly resolve and control the situation," said Hong, the Foreign Ministry spokesman.

Meanwhile, Natsuo Yamaguchi, party leader of the pacifist New Komeito, the junior coalition partner of the ruling Liberal Democratic Party, will start a four-day journey to China on Tuesday.

Yamaguchi has told reporters that he will carry a handwritten letter from Japanese Prime Minister Shinzo Abe, the hawkish president of the LDP. The letter is intended for Xi Jinping, China's top political leader and head of the military.

In a Monday interview with Hong Kong-based Phoenix TV, Yamaguchi stressed the importance of politicial dialogue between both sides, and he said he believed that Abe is ready to resume a leadership summit between the world's second- and third-largest economies.

The party leader also urged both sides not to send military aircraft into the airspace above the islands.

Feng Wei, an expert on Japanese studies at Fudan University in Shanghai, said Yamaguchi's trip is "clearly a signal" sent by Tokyo that the tension might be eased in the future.

"Yamaguchi's Beijing voyage is another presentation of Abe's ice-breaking plan, and the New Komeito party has endured a lasting bond with Beijing in the past few decades," Feng said.

The pacifist party played an indispensable role in the preparation for normalizing diplomatic ties more than 40 years ago, as key members of the party visited China with constructive proposals before the final normalization in 1972 was achieved.

"Yamaguchi has objected to Abe's high-profile plan to revise the country's pacifist Constitution, and the party leader has also told media that it is not sensible to impact Japan-China ties due to the Diaoyu Islands dispute," Feng said.

Zhou Yongsheng, the Japanese studies expert, said both Tokyo and Beijing are expected to take a good chance.

"If Tokyo makes only verbal communications with Beijing during Yamaguchi's trip yet offers no tangible concessions, I'm afraid the visit will not be constructive," Zhou warned.