BEIJING — The United States has been briefing its allies in Asia on plans to conduct naval patrols near artificial islands built by China in the disputed South China Sea, a move that could escalate tensions with Beijing after President Xi Jinping’s recent visit to Washington, American and Asian officials have said.

The “freedom of navigation” patrols, which would come within 12 nautical miles of at least one of the islands, are intended to challenge China’s efforts to claim large parts of the strategic waterway by enlarging rocks and submerged reefs into islands big enough for military airstrips, radar equipment and lodging for soldiers, the officials said.

Though China claims much of the South China Sea as sovereign territory, the 12-mile zone around the new islands is particularly delicate because international law says such artificial islands do not have sovereign rights up to the 12-mile limit.

The United States has refrained from venturing that close to Chinese-occupied islands in the South China Sea since at least 2012. In May, a United States Navy surveillance plane flew near three of China’s five artificial islands but did not go within their 12-mile territorial zones. Chinese Navy radio operators warned the Americans to leave the area.