The two Koreas exchanged warning shots along their disputed western maritime boundary, their militaries said, amid heightened tensions over North Korea's recent barrage of weapons tests.

Key points:

• South Korea says its navy broadcast warnings and fired shots to repel a North Korean merchant ship that, it says, violated the two countries' maritime boundary
• North Korea's military says it responded by firing 10 rounds of artillery shells
• The poorly marked maritime boundary is a source of long-running animosity between the Koreas

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 said, violated the sea boundary early Monday.

However, North Korea's military said it responded by firing 10 rounds of artillery shells as a warning to South Korea.

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 launches breached a 2018 inter-Korean accord on reducing military animosities and undermined stability on the Korean Peninsula.

It said the North Korean shells did not land in South Korean waters.

There were no reports of clashes between the Koreas.

The poorly marked maritime boundary off the Korean Peninsula's west coast is a source of long-running animosity between the Koreas.

It has been a scene of several bloody inter-Korean naval skirmishes and violence in recent years, including two attacks in 2010 that killed 50 South Koreans.

However, in recent weeks, North Korea has carried out a string of weapons tests in response to what it calls "provocative military drills" conducted by South Korea and the United States.

Since September 25, North Korea has fired 15 missiles and hundreds of artillery shells toward the sea.

The missile launches were largely designed to protest US-South Korean training near the Korean Peninsula, which involved a US aircraft carrier for the first time in five years.

North Korea said its artillery-firing drills were staged as countermeasures against similar South Korean artillery drills at border areas.

Seoul and Washington routinely conduct military drills to maintain their readiness against potential North Korean aggression.

The allies say their drills are defensive in nature, but North Korea views them as an invasion rehearsal.

South Korea's military is participating in annual field exercises that are set to end this Friday. This year's drills involve an unspecified number of US troops.

Next week, South Korea and the United States are to hold joint air force drills involving some 240 warplanes, including F-35 fighters operated by both nations.

The drills are aimed at inspecting the two countries' joint operation capabilities and at improving combat readiness, the South Korean military said.

Some experts say North Korea's recent missile tests suggest its leader, Kim Jong