SEOUL, South Korea: In a development that raises concern about possible clashes after North Korea's recent barrage of weapon tests, North and South Korea exchanged warning shots Monday along their disputed western sea boundary.

South Korea's navy broadcast warnings and fired warning shots to repel a North Korean merchant ship that violated the sea boundary at 3:42 a.m., the Joint Chiefs of Staff said in a statement.

North Korea's military said its coastal defence units responded by firing 10 rounds of artillery warning shots toward its territorial waters, where "naval enemy movement was detected." It accused a South Korean naval ship of intruding into North Korean waters on the pretext of cracking down on an unidentified ship.

There were no reports of fighting, but the sea boundary of the Korean Peninsula's west coast is a source of long-running animosities.

The American-led U.N. command drew a boundary at the end of the 1950-53 Korean War, but North Korea insists upon a boundary that encroaches deeply into waters controlled by the South.

Among the deadly events that have happened in the area are the North's shelling of a South Korean island and its alleged torpedoing of a South Korean navy ship, both in 2010. The two attacks killed 50 South Koreans.

Cheong Seong-chang, an analyst at South Korea's private Sejong Institute, said North Korea may have deliberately planned the ship intrusion.

Cheong said North Korea has become more bold in its recent missile tests, which it has said will use strategic nuclear weapons to strike South Korean and U.S. targets.

He noted Pyongyang would also know Washington's strained relations with Russia and China make it more difficult for the U.S. to draw cooperation from the two regional powers on the North Korean issue.

South Korea's Joint Chiefs of Staff said Monday that North Korean artillery fire violated the 2018 inter-Korean agreement to reduce military hostilities and undermined stability on the Korean Peninsula.

The General Staff of the North Korean People's Army accused South Korea of ​​provoking animosities near their land border as well as with its own artillery tests and propaganda loudspeaker broadcasts.

South Korea has already confirmed that it performed artillery firings last week as part of its regular military exercises but denied that it resumed the loudspeaker broadcasts that both Koreas halted under the 2018 agreement.

Some observers say North Korea could extend its tests, conduct its first nuclear test in five years or conduct other provocations near the West Sea border or elsewhere as South Korean and U.S. troops continue joint military exercises.