North Korea, which says the exercises are a rehearsal for war, demanded in rare talks with South Korean officials on Wednesday that the drills be postponed so they do not overlap with the planned reunion of families separated since the 1950-53 Korean War.
But Mr Kerry said: "The US doesn't believe it is appropriate to link humanitarian issues such as (family) reunification to any other issues."
South Korea said it had rejected North Korea's demand to postpone the exercises which had raised the possibility the family reunions might be scrapped.
North and South Korean officials will meet again today for a second round of talks at the Panmunjom truce village.
Mr Kerry urged North Korea to abide by commitments it had made to show it was serious about re-engaging the US in nuclear talks.
He also said China could do more to help nudge North Korea into line.
Mr Kerry said: "Our belief is China can do more to urge North Korea to begin taking action to come into compliance with its international obligations and I will encourage China to use all means at its disposal to do so."
He is due in China today for talks on a controversial air defence zone declared by Beijing last year.