U.S. Democratic presidential candidate John Kerry has pledged that if elected president, he would seek one-on-one talks with North Korea on its nuclear program.

In a major speech on national security in the battleground state of Iowa Wednesday, Kerry accused President George W. Bush of sitting by and allowing Pyongyang's nuclear arsenal to rise from two nuclear weapons to six or eight bombs.

He said he will work with U.S. allies to get the six-way nuclear talks back on track and directly hold talks with the North as Seoul and Beijing have requested Washington to do.