North Korea on Tuesday threatened the United States and South Korea over joint naval drills taking place this week in tense Yellow Sea waters ahead of a Washington summit by the allies' leaders.

In a highly conditional warning, the section of the Korean People's Army responsible for operations in North Korea's southwest said it will hit back if any shells fall in its territory during the drills, which began Monday and will end Friday. Should the allies respond to that, the statement said, Pyongyang's military would then strike five South Korean islands that stand along the aquatic frontline between the countries.

The area includes waters that are claimed by both countries, and is the most likely scene of any future clash between the rival Koreas. North Korea disputes a boundary unilaterally drawn close to its shores by the U.S.-led U.N. Command after the war, and has had three bloody naval clashes with the South since 1999.

Highly critical language is standard from North Korea during what the allies call routine military drills that they stage over the course of a year. Tuesday's statement was softer than the bellicose rhetoric Pyongyang unleashed with regularity during two months of larger-scale joint military drills by the allies that ended one week ago. That included threats of nuclear and missile strikes on Washington and Seoul.

Still, this new warning comes at a time of tentative diplomatic maneuvering on the divided Korean Peninsula, which is still technically in a state of war, as the three-year Korean War ended 60 years ago in an armistice, not a peace treaty.

The threat also came hours ahead of a summit by U.S. President Barack Obama and South Korea's new president, Park Geun-hye. They hope to present a strong front against North Korea during their meeting Tuesday at the White House, but also want to leave the door open to talks with Pyongyang.

There are concerns that any skirmish or shelling between the Koreas could escalate into war. Two attacks blamed on Pyongyang in 2010 killed 50 South Koreans, and Park has repeatedly said Seoul would respond aggressively to another attack from the North.

If Pyongyang conducts an attack similar to the 2010 shelling of an island that killed four South Koreans, "We will make them pay," Park told CBS in an interview aired Monday.

Inter-Korean relations are particularly strained amid North Korean anger over U.S.-South Korean military drills and U.N. sanctions in March that sought to punish the North over its February nuclear test, the country's third.

Last week, South Korea pulled out its last remaining citizens from a joint factory park in North Korea after Pyongyang withdrew all of its 53,000 workers earlier. The park is the last symbol of inter-Korean rapprochement.

Despite the allies' claims that the military drills are routine, Pyongyang calls them invasion preparation and is especially sensitive to the inclusion of any U.S. nuclear-capable assets. Washington in March responded to rising tensions on the Korean Peninsula by making the unusual announcements that it had sent nuclear capable B-52 and B-2 bombers to participate in the drills, prompting a harsh North Korean rhetorical response.

Nuclear-powered U.S. carriers routinely come to South Korea around this time of year as part of drills aimed at enhancing naval cooperation, South Korean Defense Ministry spokesman Kim Min-seok said Monday in a briefing. But Seoul wouldn't discuss whether any U.S. nuclear capable assets were participating in this week's drills, and U.S. military officials declined to comment on operations.

On Tuesday, Kim denied North Korea's claim that South Korea's military this week conducted live-fire artillery drills near the disputed Yellow Sea waters.

Kim also said the South Korean military is keeping an eye on any movements of a North Korean mid-range missile on the east coast that's capable of potentially hitting Guam. South Korean officials said last month that the North was prepared to test the missile at any time.

Kim said Seoul would confirm if North Korea completely withdraws the missile, which officials earlier said the North seemed poised to test. He said he couldn't share any other details.