SEOUL, South Korea — The rival Koreas exchanged warning shots along their disputed western sea boundary on Monday, their militaries said, amid heightened animosities over North Korea’s recent barrage of weapons tests.

South Korea’s Joint Chiefs of Staff said in a statement that its navy broadcast warnings and fired warning shots to repel a North Korean merchant ship that it says violated the sea boundary early Monday.

North Korea’s military said its coastal defense 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 navy ship of intruding into North Korean waters on the pretext of cracking down on an unidentified ship.

South Korea’s Joint Chiefs of Staff said the North Korean artillery firings breached a 2018 inter-Korean accord on reducing military animosities and undermines stability on the Korean Peninsula. It said the North Korean shells didn’t land in South Korean waters but South Korea is boosting its military readiness.

There were no reports of clashes between the Koreas, but the poorly marked sea boundary off the Korean Peninsula’s west coast is a source of long-running animosities between the Koreas. It’s a scene of several bloody inter-Korean naval skirmishes and violence in recent years, including the North’s shelling of a South Korean island and its alleged torpedoing of a South Korean navy ship that killed a total of 50 people in 2010.

In recent weeks, North Korea has carried out a string of weapons tests in response to what it calls provocative joint military drills between South Korea and the United States. Some observers say North Korea could extend its spate of testing or launch provocations near the western sea border as South Korean and U.S. militaries are continuing their combined military exercises.

Washington and Seoul had scaled back or canceled their regular drills in recent years to support their now-dormant nuclear diplomacy with North Korea or guard against the COVID-19 pandemic. But the allies have been reviving or expanding those trainings since the May inauguration of conservative South Korean President Yoon Suk Yeol, who vows a tougher stance on North Korean provocation.

In its Monday statement, the General Staff of the North’s Korean People’s Army accused South Korea of provoking animosities near their land border as well with its own artillery tests and propaganda loudspeaker broadcasts. South Korea has already confirmed it performed artillery firings last week as part of its regular military exercises, but didn’t immediately respond to the North’s claim on the loudspeaker broadcasts.

“The KPA General Staff once again sends a grave warning to the enemies who made even naval intrusion in the wake of such provocations as the recent artillery firing and loudspeaker broadcasting on the ground front,” the North’s statement said.