China has pressed Japan not to broach Beijing’s disputes with regional neighbors in the South China Sea at the upcoming Group of Seven summit to be held in Japan in May, arguing that touching on the issue would hamper efforts to improve bilateral relations, diplomatic sources said Saturday.

China pressed the point to Japan at a vice foreign ministerial gathering held in Tokyo in late February, according to the sources.

But Japan rebuffed the Chinese demand, saying the international community cannot accept China’s building of artificial islands in the sea and their militarization, they said.

China is embroiled in overlapping territorial and maritime disputes in the South China Sea with Taiwan and four members of the Association of Southeast Asian Nations — Brunei, Malaysia, the Philippines and Vietnam.

Prime Minister Shinzo Abe is eager to clearly state the importance of the rule of law in the G-7 leaders’ declaration after securing unity over the South China Sea issue at the G-7 foreign ministers’ meeting that will take place in Hiroshima in April.

If Japan does raise the issue at the summit, Chinese ire could cast a pall over budding signs of improvement in bilateral ties marred by a territorial spat surrounding islands in the East China Sea.

This year’s summit of the G-7 states — Britain, Canada, France, Germany, Italy, host Japan and the United States — is set to take place in Mie Prefecture on May 26-27.

At a meeting with Shinsuke Sugiyama, Japan’s deputy foreign minister for political affairs, at the Foreign Ministry in Tokyo on Feb. 29, Kong Xuanyou, an assistant Chinese foreign minister, voiced strong discontent with Tokyo’s open criticism of Beijing over the South China Sea issue, according to the sources.

Kong was quoted as telling Sugiyama that Japan, which is not involved in the disputes, is acting like a concerned party. He also expressed doubt about whether Tokyo really wants to improve relations with Beijing.

Ties between the two nations sank to the lowest point in years following the Japanese government’s purchase in September 2012 of most of the Senkaku Islands in the East China Sea from a private Japanese owner. But they have gradually warmed since Abe and Chinese President Xi Jinping held their first meeting in November 2014.

The Chinese diplomat went on to warn that how Japan approaches the issue at the G-7 summit will be a litmus test of whether bilateral ties can be improved and that China will be watching closely, the sources said.

Sugiyama responded that it would be intolerable to try to change the status quo in the South China Sea with military might and that it would serve the international community’s common interest to establish the rule of law in the sea.

Kong showed optimism on Foreign Minister Fumio Kishida’s planned visit to China, possibly this spring, but was cautious about fixing the schedules of a trilateral summit between Japan, China and South Korea or a foreign ministerial meeting to be held in Japan this year.

Kong and Sugiyama also exchanged views on differing perceptions of history.

The Chinese diplomat accused Japan of not showing sincerity about historical issues, citing Sugiyama’s remark at a U.N. panel in February that Tokyo has found no documents confirming that so-called comfort women were forcefully recruited by military or government authorities during World War II.

The South China Sea issue was dwelt upon when Kishida and his Chinese counterpart Wang Yi held telephone talks last Monday. Wang called for Tokyo’s constructive efforts to improve bilateral relations, according to the Chinese Foreign Ministry.