North Korea fired more short-range missiles away from South Korea and into the East Sea on Monday, its third successive day of missile tests.
"North Korea again launched a short-range projectile that appears to be a KN-02 (surface-to-surface) missile," said an unidientified ministry official. "We are closely watching the movements of the North's military in case of further launches."
The North routinely tests short-range missiles, but its bellicose rhetoric and threats of nuclear war against the United States and South Korea have put the region on edge.
"Whether it's a test-firing or armed demonstration, North Korea should not engage in tension-creating acts," said Kim Jang-soo, head of South Korea's national security office.
In recent weeks a relative calm had appeared to settle tensions, especially after the US and South Korea ended their annual Foal Eagle military exercises on April 30. But now the North has begun its military drills, firing three short-range guided missiles on Saturday, and one more on Sunday.
"We are conducting intense military exercises to strengthen our defense capacity," said North Korea's state-run Korean Central News Agency (KCNA), quoting the Committee for the Peaceful Reunification of Korea. "Our military is conducting these exercises in order to cope with the mounting war measures from the US and South Korea, which is the legitimate right of any sovereign country."
Pyongyang also said in a statement that it was "brigandish sophism' for South Korean and US officials to criticize them for destabilizing relations with new missile tests, especially after their more extensive joint military drills.
On Sunday, United Nations Secretary General Ban Ki-moon called on North Korea to halt further "provocative" missile tests.
"I hope that North Korea will refrain from further such actions," Ban said, adding, "It is time for them to resume dialogue and lower the tensions. The United Nations is willing to help."
In February, Pyongyang exploded its third underground nuclear bomb. In response, the UN Security Council slapped the impoverished nation with a new round of sanctions. Since then, the US and its allies have called on North Korea to dismantle its nuclear program, something Pyongyang has so far explicitly refused to do.