"China is strongly dissatisfied with relevant moves taken by G7," foreign ministry spokesman Lu Kang said in a statement.
"We urge G7 members to abide by their promise of not taking sides on territorial disputes, respect the efforts by regional countries, stop all irresponsible words and actions, and make constructive contribution to regional peace and stability."
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A two-day meeting of G7 foreign ministers -- a grouping that excludes China -- in the Japanese city of Hiroshima issued a joint statement saying: "We are concerned about the situation in the East and South China Seas, and emphasise the fundamental importance of peaceful management and settlement of disputes.
"We express our strong opposition to any intimidating, coercive or provocative unilateral actions that could alter the status quo and increase tensions."
The G7 statement did not explicitly name China, but Beijing lays claim to almost all of the South China Sea despite conflicting partial claims from Brunei, Malaysia, Vietnam, Taiwan and the Philippines.
It has constructed artificial islands in the area in recent months as it asserts its sovereignty.
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Japan, meanwhile, has its own dispute with China in the East China Sea over uninhabited islands that it administers but that are also claimed by Beijing.
The G7 also urged "all states to refrain from such actions as land reclamations" and "building of outposts... for military purposes".
Beijing indicated that it felt targeted by the comments.
"Given the sluggish global economic recovery at the moment, G7 should have focused on global economic governance and cooperation instead of hyping up maritime issues and fuelling tensions in the region," Chinese foreign ministry spokesman Lu said.
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