The United States and South Korea are conducting joint naval drills this week

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.

Still, this new warning comes at a time of tentative diplomatic manoeuvring 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 Mr 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,” Mr 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.

More In: World | International | News