Former U.S. President Bill Clinton expressed concern in Tokyo on Thursday about the geopolitical situation on the Korean Peninsula.

He urged Japan, the U.S., South Korea and China to work together, saying North Korea has the capability to annually manufacture six or seven missiles capable of delivering a nuclear warhead, which it could then sell.

Clinton recalled that he had wanted to travel to Pyongyang to seal a deal on North Korea's nuclear program toward the end of his presidency but was unable to because he was occupied with the Israeli-Palestinian conflict.

He made these remarks in talks with Toshiaki Ogasawara, chairman and publisher of The Japan Times, at the Four Seasons Hotel.

Clinton is in Japan to promote the humanitarian work of the William J. Clinton Presidential Foundation.