Japanese defense officials warned their Chinese counterparts over further possible intrusions of Japan's airspace by Chinese spy balloons and demanded that no such incidents happen again during their talks in Tokyo on Tuesday.

While tensions linger over suspected Chinese spy balloons spotted over Japan in recent years, the two sides pledged to continue working together for the planned launch of a hotline between defense authorities around the spring to avoid unexpected military incidents.

Japanese and Chinese defense and foreign ministry officials have kicked off a series of talks in Tokyo from Tuesday, as the neighboring countries seek to improve their strained relations and promote exchanges to stimulate their economies hit hard by the coronavirus pandemic.

The meeting between defense authorities on Tuesday were joined by Atsushi Ando, deputy director general of the Japanese Defense Ministry's Defense Policy Bureau, and Zhang Baoqun, deputy director of the Office for International Military Cooperation of the Chinese Central Military Commission.

Diplomats including Japan's Senior Deputy Foreign Minister Shigeo Yamada and China's Vice Foreign Minister Sun Weidong also held a meeting in Tokyo the same day.

They agreed to continue to closely communicate at "various levels" toward building "a constructive and stable" bilateral ties, according to the Japanese Foreign Ministry.

On Wednesday, the two governments are set to hold a security dialogue involving their senior foreign affairs and defense officials, in what would be their first such meeting since February 2019 when it was held in Beijing.

The talks are taking place a week after the Japanese Defense Ministry said that at least three unidentified flying objects spotted over the nation's territorial airspace in three years from 2019 are "strongly suspected" to have been Chinese unmanned spy balloons.

China has denied the allegation, criticizing Japan for "making up stories to smear and attack" Beijing without clear evidence and urging Tokyo to refrain from following Washington's lead in using the incidents to hype up Chinese threats.

Japanese defense officials said Tuesday that violations of Japan's territorial skies by balloons are "unacceptable" and urged China to get to the bottom of the incidents, according to a Japanese Defense Ministry official.

The two Asian powers have been at odds over issues such as the Tokyo-controlled, Beijing-claimed Senkaku Islands, which China calls Diaoyu. Chinese coast guard vessels have repeatedly entered Japanese waters around the uninhabited islets in the East China Sea.

As part of efforts to stabilize their bilateral ties, Japanese Prime Minister Fumio Kishida and Chinese President Xi Jinping agreed in November last year on an early start of the defense hotline during their meeting in Bangkok.

In 2018, Japan and China launched the Maritime and Aerial Communication Mechanism to avoid accidental clashes at sea and in the air. Opening a direct hotline is expected to be a pillar of the communication mechanism, but it has yet to be realized.

Meanwhile, according to several sources familiar with Japan-China relations, China's Communist Party has repeatedly requested that it wants to resume a dialogue with Japan's ruling Liberal Democratic Party and its coalition partner Komeito, which was last held in 2018.

Liu Jianchao, head of the International Liaison Department of the Communist Party, told Komeito leader Natsuo Yamaguchi in December and Japanese Ambassador to China Hideo Tarumi in January the party is eager to restart in-person exchanges between ruling party officials of the two countries, the sources said.

The next round of talks are expected to be held in China with major agenda items including security, economy and people-to-people exchanges.

Yamaguchi was scheduled to visit China in January, but his trip did not materialize as Beijing criticized Tokyo's tightening of border controls on visitors from mainland China amid a surge of coronavirus infections in the country.