North Korean leader Kim Jong Un ordered his troops to practice firing artillery near a disputed sea boundary with rival South Korea, Pyongyang’s state media reported Monday, drawing a quick rebuke from Seoul. It was the latest sign of impatience from Kim amid worries that nearly two years of US-North Korean diplomacy will fall apart if Washington doesn’t meet Pyongyang’s year-end deadline to offer a new initiative to settle their long-running standoff over the North’s nuclear weapons program. The coastal artillery company’s actions during Kim’s visit to the west coast’s Changrin Islet “fully showed their gun firing skills” and “delighted the supreme leader,” according to the North’s Korean Central News Agency. It didn’t say when the visit took place, and it wasn’t clear what specific weapons were fired. Seoul’s Unification Ministry said it was Kim’s first known trip to a front-line military unit since at least April last year, around the start of his diplomatic engagement with the US Those once-promising negotiations are largely at a standstill now as North Korea steps up pressure on Washington to lift international sanctions and abandon what it calls hostile policies against the North. When North Korea has previously spoken of removing US hostility, it has meant the presence of tens of thousands of US troops stationed in South Korea and Japan. Kim is believed to want a deal that provides relief from crippling sanctions against his country in return for disarmament moves that critics say would come too slowly and wouldn’t significantly roll back his nuclear program. The islet where the recent drills took place is just north of the de facto inter-Korean maritime boundary, the scene of several bloody naval skirmishes between the rivals. In 2010, North Korea launched an artillery strike on a South Korean island just south of the boundary, killing four people. Earlier that year, North Korea is accused of torpedoing a South Korean warship operating near the boundary, killing 46 sailors. South Korea’s Defense Ministry expressed regret over the latest drills, saying they violated deals settled between the Koreas last year that looked to lower military animosities along the border. Spokeswoman Choi Hyun-soo told reporters that North Korea must stop any acts that will increase military tensions and abide by the past agreements. Relations between the two Koreas improved greatly last year as Kim engaged in talks with the US over the fate of his advancing nuclear arsenal. Kim met President Donald Trump in Singapore in June last year in what was the first such North Korea-US summit since the end of the 1950-53 Korean War. Kim also met South Korean President Moon Jae-in three times last year.