South Korean officials say Pyongyang has failed to respond to phone calls, just weeks after the two countries restored hotlines.

This comes one day after a high-ranking  North Korean official said Seoul should pay a price for holding joint military exercises with the United States. 

Kim Yo-jong, who is also the sister of North Korean leader Kim Jong-un, also warmed the North would strengthen its pre-emptive strike capabilities.

On Tuesday, South Korea and the U.S. began preliminary training for their annual war games, and larger, computer-simulated exercises will begin next week.

The drills have increased tensions just weeks after the hotlines were restored.

The lines were restored last month after South Korean President Moon Jae-in and Kim Jong-un pledged to restore ties.

North Korea views the war games as a rehearsal for an invasion of its land. Pyongyang says its nuclear weapons program is needed for defensive purposes.