US Vice President Joe Biden spent an hour trying to persuade Japan's prime minister not to visit the controversial Yasukuni Shrine, two weeks before a pilgrimage that sparked fury in Asia, a report said Wednesday.
In a telephone conversation with Prime Minister Shinzo Abe on December 12, Biden repeatedly urged the Japanese premier to stay away from the shrine, Kyodo News said, quoting unnamed diplomatic sources.
Yasukuni is a memorial to around 2.5 million war dead, but is controversial because those commemorated include a number of senior figures condemned to death at the end of World War II for their role in directing the conflict.
"I will decide by myself whether I will go," Abe reportedly responded, during what Kyodo said was a "tense" conversation with the US vice president. Biden finally gave up, saying he would leave the decision to the prime minister, the agency added.
Immediate confirmation of the report was not available.
Abe's December 26 trip to the shrine drew condemnation from China and South Korea, who view visits there as a symbol of what they say is Japan's unwillingness to come to terms with its wartime aggression.
The shrine is also controversial because of an attached museum that offers a narrative of the war most historians find unacceptable, and which presents Japan as a frustrated liberator and a victim, rather than an aggressor.
Washington also issued a rebuke after Abe's visit, saying it was "disappointed" by Abe's action.
US diplomats privately acknowledge they were surprised by the move and say they had made their opinions known to the prime minister's office in advance.
But the news that personal overtures from Joe Biden, who has enjoyed a good working relationship with senior Japanese figures, were rejected will be an embarrassment to the White House.
Abe has defended his visit to Yasukuni as "natural" and said he had no intention of hurting the feelings of Chinese or Koreans.
The Japanese prime minister has not held a summit with Chinese president Xi Jinping or South Korean President Park Geun-Hye since taking office in December 2012, with Tokyo locked in separate sovereignty disputes with its neighbours.
The parlous state of relations in northeast Asia is a headache for the US, which would like allies Japan and South Korea to get along, in part to help provide a counterweight to China's growing military and economic might.
The spat between Tokyo and Beijing over uninhabited islands in the East China Sea has seen regular paramilitary standoffs and the increasing use of military planes and vessels, albeit at arm's length thus far.
Observers warn it is a key geopolitical fracture point, with some suggesting the spat could descend into a conflict that would have disastrous economic consequences, possibly on a global scale.
At the World Economic Forum in Davos last week, Abe cause a stir when he drew a comparison between current Sino-Japanese relations and those between Britain and Germany in the run-up to World War I.
US President Barack Obama is expected to tour Asia in April and although no destinations have been announced, it is thought likely that he will stop in Tokyo, where regional tensions will be high on the agenda.