Japan, America's closest ally in Asia, has been trying to send a message to U.S. presidential hopeful Donald Trump: don't try to strike any deal with China that could upend years of collective efforts to rein in Beijing and risk the region's fragile peace.

Tokyo has stepped up attempts to engage with people close to Trump in recent weeks, as the 77-year-old's victories in Republican primaries in Iowa and New Hampshire have seen him emerge in some polls as the front-runner in November's presidential election.

The outreach — detailed in interviews with six Japanese officials, much of it previously unreported — comes as Prime Minister Fumio Kishida prepares for an April state visit to the United States at U.S. President Joe Biden's invitation.