Police have warned of stern action against ungrounded rumors about a North Korean attack which have been spreading online this week and further anxiety amid military tensions on the peninsula.“We will take appropriate countermeasures to prevent these false Internet rumors from triggering unnecessary panic,” National Police Agency chief Lee Sung-han said Thursday at a nationwide senior police officials’ meeting in Seoul.Early Wednesday, an urgent message appeared on Twitter that North Korea was shelling Yeoncheon Island, Gyeonggi Province, near the inter-Korean border.“A battle broke out in Yeoncheon. F-15K fighter jets are currently on stand-by. Citizens of Gyeonggi Province are evacuating,” the post read.The rumor circulated fast on the micro-blogging service and other social network sites, making Yeoncheon one of the most frequently searched words on Internet portals until Thursday morning.Cases of smishing ― a phishing scam operated by sending multimedia text messages ― taking advantage of heightened security concerns were also reported.Citizens in Seoul and Gyeonggi Province received cell phone messages from 112, the police hotline number, that claimed to be an image file of North Korea’s attack on Yeonpyeongdo Island.When the recipients opened the link in the message, they found an unrelated picture. No case of financial damage has been reported yet.Some netizens claimed that if a war breaks out, all sports utility vehicle owners must provide their cars to the military. Others claimed they wanted a war to break out, and posted pictures of military equipment they had purchased such as military daggers or emergency rations.Police cautioned citizens not to open suspicious text messages with such content and vowed to track down and punish rumor-mongers.By Yoon Min-sik and Lee Sang-ju