"We are concerned about the situation in the East and South China Seas, and emphasize the fundamental importance of peaceful management and settlement of disputes," the G7 diplomats wrote in a joint statement at the end of their two-day meeting in Hiroshima, Japan on Monday.
"We express our strong opposition to any intimidating, coercive or provocative unilateral actions that could alter the status quo and increase tensions", they added.
Parts of the South China Sea are claimed in turn by Malaysia, Vietnam, Taiwan, Brunei and the Philippines, but Beijing continues to assert its dominion over almost the whole area. To this end, China has boosted its military presence in the body of water and launched a series of controversial land reclamation projects.
Without mentioning China by name, G7 called on "all states to refrain from such actions as land reclamations," for example the "building of outposts... for military purposes."
Chinese Foreign Ministry spokesman Lu Kang responded by saying he had not read the document, but cautioned the G7 from showing prejudice against Beijing.
Kerry described his visit to a museum documenting the effects of the nuclear attack as "gut wrenching"
Kerry 'deeply moved' by Hiroshima memorial
Earlier in the day, US Secretary of State John Kerry took the opportunity to make an unprecedented visit to a memorial in Hiroshima dedicated to the victims of the Americans' atomic bomb attack in World War II. Kerry is the highest-ranking US official to pay his respects at the spot where the nuclear warhead fell.
Some 140,000 people died after the blast on August 6, 1945, either in the immediate aftermath or later from radiation poisoning. The city was home to a key military installation, but the majority of the victims were civilians.
"I want to express on a personal level how deeply moved I am to be the first US secretary of state to visit Hiroshima," Kerry told the press.
"Everyone should visit Hiroshima, and everyone means everyone," the Secretary of State continued, "I hope one day the president of the United States will be among the everyone who is able to come here."
Kerry did not confirm rumors, however, that President Obama is mulling a trip to the memorial when he arrives later in the week for a meeting of G7 leaders in another part of Japan.
es/kms (AFP, dpa)