A senior US envoy has warned that ties with Japan could be affected in many fields if Tokyo missed a May deadline for solving a dispute over an American military base.<br/><br/>The US Assistant Secretary of State for East Asian and Pacific affairs Kurt Campbell, who met two lawmakers from Japan's opposition Liberal Democratic Party (LDP) in Washington ahead of his tour of Asia, said if the relocation is not decided by May, the relationship could be affected in many fields. <br/><br/>Campbell told the lawmakers he wants to see progress in the dispute over the next few weeks. <br/><br/>Japan's centre-left prime minister, who has pledged to make the final decision by May, said his government would decide by the end of March on a basic plan for the relocation. <br/><br/>The US envoy is scheduled to visit Japan as part of his Asian tour beginning tomorrow.