Prime Minister Junichiro Koizumi said Monday he will urge U.S. President George W. Bush to make more diplomatic efforts in order to gain international support for a possible U.S. attack on Iraq.

Koizumi said the message he plans to convey to Bush when he meets him in New York on Thursday is that: "International cooperation and legitimacy are essential in any war."

Koizumi was speaking to reporters aboard a Japanese government jet while en route from Tokyo to Boston for a five-day visit to the U.S. The prime minister arrived in Boston in the afternoon and was to leave for New York on Tuesday morning.

Among major U.S. allies, British Prime Minister Tony Blair has voiced clear support for U.S. plans to wage war on Iraq, but France and Germany are taking a more cautious stance.