SEOUL – South Korea’s military fired warning shots after North Korean soldiers crossed the rivals’ tense border on Tuesday, South Korean officials said.

South Korea’s military said in a statement that about 10 North Korean soldiers returned to the North after South Korea made warning broadcasts and fired warning shots. It said the North Korean soldiers violated the military demarcation line at the eastern section of the border at 5 p.m.

South Korea’s military said it is closely monitoring North Korean activities.

Bloodshed and violent confrontations have occasionally occurred at the Koreas’ heavily fortified border, called the Demilitarized Zone. But when North Korean troops briefly violated the border in June last year, it didn’t escalate into a major source of tensions as South Korean officials assessed the soldiers didn’t deliberately commit the border intrusion.

The motive for Tuesday’s border crossing by North Korean soldiers wasn’t immediately clear.

Animosities between the Koreas are running high now as North Korean leader Kim Jong Un continues to flaunt his military nuclear capabilities and align with Russia over President Vladimir Putin’s war on Ukraine. Kim is also ignoring calls by Seoul and Washington to resume denuclearization negotiations.

Since his Jan. 20 inauguration, U.S. President Donald Trump has said he would reach out to Kim again to revive diplomacy. North Korea has not responded to Trump’s remarks and says U.S. hostilities against it have deepened since Trump’s inauguration.

South Korea, meanwhile, is experiencing a leadership vacuum after the ouster of President Yoon Suk Yeol last week over his ill-fated imposition of martial law.