Danny Russel, the top US diplomat on East Asia, said he made the suggestion as "food for thought" and not as a formal proposal as he met regional counterparts in Myanmar to prepare for a regional summit later this year.
"The claimant states themselves could identify the kind of behaviour that they each find provocative when others do it, and offer to put a voluntary freeze on those sorts of actions on the condition that all the other claimants would agree to do so similarly," Russel, an assistant secretary of state, told reporters on a conference call.
The United States has pushed for years for a code of conduct to lay out rules to prevent the escalation of incidents in the South China Sea, an economically vital waterway in which China has overlapping claims with several other nations.
But Russel acknowledged that tensions have been "going up quickly" in the sea. Riots erupted in Vietnam last month in anger against China's deployment of an oil rig in contested waters.
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Russel said that the Chinese delegation at the talks in Myanmar offered a "spirited and vigorous defence" of its position, but voiced hope that Beijing understood that other nations' statements were "offered not in the spirit of condemnation, but in the spirit of compromise."
President Barack Obama is expected to travel to Myanmar in November for the East Asia Summit on his second visit to the country formerly known as Burma, a onetime Western pariah which has embraced democratic reforms.