SEOUL, South Korea - Tempers flared Friday as North Korea warned South Korea to cancel artillery drills planned for the same island the North shelled in November, pledging it would answer any provocation with a strike even harsher than last month's deadly attack.

Sometime between Saturday and Tuesday, Seoul plans a live-ammunition drill on Yeonpyeong island, where similar drills Nov. 23 prompted a Northern artillery barrage that killed four people.

The North's state-run Korean Central News Agency reported Friday that officials in Pyongyang sent a notice to Seoul warning that drills on the island would bring "unpredictable self-defensive strikes." The notice added that "the intensity and scope of the strike will be more serious than the Nov. 23" shelling, the news agency said.

North Korea dismissed the drills as an effort to "save the face of the South Korean military, which met a disgraceful fiasco" in the shelling of Yeonpyeong, the news agency reported.

But South Korea pledged Friday to carry out the exercises, which Defense Ministry officials characterized as part of "routine, justified" exercises for its own defense.

Many fear that the newest belligerence from North Korea may signal a possible slide closer to war.

"What you don't want to have happen out of that is for us to lose control of the escalation," Gen. James Cartwright, vice chairman of the U.S. Joint Chiefs of Staff, told reporters in Washington.

The Obama administration has supported Seoul's planned drills, saying they posed no threat to the North. "North Korea should not see these South Korean actions as a provocation," State Department spokesman P.J. Crowley said Thursday.

But in Moscow, Russian Deputy Foreign Minister Alexei Borodavkin summoned U.S. and South Korean envoys Friday to urge the South "to refrain from the planned firing to prevent further escalation of tension in the Korean peninsula," according to a ministry bulletin.

The most recent back-and-forth between the Koreas came as New Mexico Gov. Bill Richardson arrived in Pyongyang on a private mission to try to ease tensions, which have been elevated since North Korea allegedly torpedoed a South Korean patrol ship in March, killing 46.

Richardson, who has in the past served as unofficial envoy to North Korea, planned a four-day visit that reportedly included a tour of the North's main nuclear complex at Yongbyon.

"My objective is to see if we can reduce the tension in the Korean peninsula," he said upon arriving in Pyongyang.