The DPJ president, who was expected to be elected prime minister Sep 16 in a parliamentary vote, said Obama congratulated the party on its elections victory, but he did not release any details of the 12-minute phone call to reporters, saying it was the request of the White House.

The White House itself said Obama pledged to work closely with Hatoyama to strengthen the global economic recovery, combat climate change, curtail North Korea's nuclear activities and confront Al Qaeda in Afghanistan.

'President Obama and Mr Hatoyama stressed the importance of a strong US-Japan alliance and their desire to build an even more effective partnership,' a White House statement said.

The DPJ won 308 of the 480 seats in the House of Representatives Sunday. It had won control of the other chamber of Japan's Diet, the House of Councillors, in 2007.