Compose the next sentence for this paragraph.

(CNN) -- The United States will talk to North Korea, but only if the country gets serious about negotiating the end of its nuclear weapons program, Secretary of State John Kerry said Friday during a visit to South Korea, a key U.S. ally. "North Korea will not be accepted as a nuclear power," Kerry said after arriving in Seoul. His trip to South Korea -- part of an Asian swing that also includes North Korean ally China -- came a day after a Pentagon intelligence assessment surfaced suggesting North Korea may have developed the ability to fire a nuclear-tipped missile at its foes.

South Korea this week accused the
North Korea of carrying out the March 20 attacks.