The U.S. envoy for North Korea once again urged Pyongyang on Sunday to engage in talks to denuclearize.
Special Representative Sung Kim called Pyongyang's recent ballistic missile test concerning and counterproductive against lasting peace in the Korean Peninsula.
But Pyongyang has so far rejected offers to return to the table, accusing Washington and Seoul of talking diplomacy while escalating tensions with their own military activities.
On Thursday, the North said the United States was overreacting to a submarine-launched ballistic missile test that it called self-defensive.
That launch was one of several in recent weeks, violating U.N. sanctions imposed on North Korea.
Kim reiterated that Washington had no hostile intent towards the North.
South Korean nuclear envoy Noh Kyu-duk, said he and the U.S. envoy had what he called a "serious" discussion of Seoul's proposal to formally declare an end to the Korean War.
The 1950-1953 Korean War ended in an armistice rather than a peace treaty.
South Korean officials see such a declaration as a gesture of goodwill to get talks started.