Responding to North Korea's fresh military threats against South Korea, the United States called on the communist nation Friday to improve inter-Korean ties.

Earlier in the day, the North's military issued a statement vowing to launch “retaliatory military attacks” against South Korea because its reserve forces used photos of North Korean leaders for target practice.

The threats were the latest in a series of hostile gestures by the North, including the disclosure of a secret meeting with the South in Beijing last month and termination of exclusive contract with a Seoul conglomerate for the Mount Geumgang tourism business.

"It's obviously not the kind of behavior that we are looking for from North Korea," State Department spokesman Mark Toner told a press briefing. "We've said that many times we are looking for North Korea to put its relations with South Korea on a more positive track."

After weeks of overtures for dialogue with Seoul, Pyongyang has been stepping up threats, especially following leader Kim Jong-il's trip to China.

Toner would not be drawn into a question on a possible link between Kim's recent China visit and Pyongyang's tougher stance.

(Yonhap News)