Seoul says North Korea has fired artillery shots during an apparent military exercise near a disputed maritime border with the South amid heightened tensions between the two neighbors. The North Korean army’s fired “a few artillery rounds” on Saturday morning from a battery at Jangsangot promontory on its southern coast, the South’s Defense Ministry said in a statement. Pyongyang “is believed to have conducted a military drill” north of the disputed sea frontline with the South, the statement added. It added that Saturday’s firing prompted Seoul to call on residents on the Baengnyeong Island to go into shelters as a precautionary measure. South Korea’s Baengnyeong sits less than 20 kilometers (12 miles) at its closest point to the North’s shore. Meanwhile, an unidentified local official from Baengnyeong Island said that residents did not evacuate, but fishing boats returned to their ports. The South Korean statement said there is now no sign of further provocative activities in the region. The incident comes at a time when the US and South Korea are preparing for their annual war games slated to begin early in March. Some 15,000 US troops are expected to take part in the two-phased exercises, known as Key Resolve and Foal Eagle. Pyongyang is irked by joint Seoul-Washington military maneuvers and views them as direct threats against its security and preparations for war. The Korean Peninsula has been locked in a cycle of military rhetoric since the 1950-1953 Korean War, which ended in an armistice. No peace deal has been signed since then, meaning that Pyongyang and Seoul remain technically at war. Tensions between the two Koreas escalated since the start of 2015 after the North’s nuclear test in January and a long-range rocket launch on February 7. Pyongyang said the rocket launch was aimed at placing an earth observation satellite into orbit. However, Washington and Seoul denounced the move as a cover for an intercontinental ballistic missile test. North Korea has vowed to develop a nuclear arsenal in an effort to protect itself from the US military, which occasionally deploys nuclear-powered warships and aircraft capable of carrying atomic weapons in the region.