North Korea conducted live-fire artillery drills Tuesday near the countries' disputed western sea boundary, South Korean military officials said, in a possible indication of rising frustration in Pyongyang as it unsuccessfully pushes for outside aid.
Both Koreas regularly conduct routine artillery drills near South Korean islands and the North Korean mainland in the Yellow Sea. But they can be sensitive because of the disputed maritime line separating the countries.
Last month, South Korea fired artillery shells into the North's waters after North Korean shells from a live-fire drill landed south of the boundary. After South Korean drills in 2010, North Korea shelled a South Korean island, killing four.
A Defence Ministry official, speaking on condition of anonymity because of office rules, confirmed that the drills had begun but provided no other details.
Analysts have said that Pyongyang's announcements of live-fire drill plans are likely linked to frustration by the impoverished country at making little progress in a recent push to win outside aid.
The so-called Northern Limit Line was drawn by the U.S.-led UN Command without Pyongyang's consent at the close of the 1950-53 Korean War, which ended with a truce, not a peace treaty, leaving the peninsula still technically in a state of war. North Korea routinely argues that the line should run farther south.
A year after threatening each other with war, the Koreas had restored some trust and held reunions earlier this year of families divided by the war. But ties have since steadily soured. Pyongyang this week launched a sexist rhetorical attack on South Korean President Park Geun-hye, calling her a "despicable prostitute."
North Korea test-fired two medium-range ballistic missiles in March into the Sea of Japan. Pyongyang had earlier staged a series of shorter-range rocket launches to protest annual springtime military drills by the U.S. and South Korea that Pyongyang says are invasion preparation.
South Korean officials have also warned the North could be preparing for its fourth nuclear test.
The North's live-fire drills come as South Korea deals with the tragedy of a ferry sinking that has left more than 300 dead or missing.