North Korea fired dozens of artillery shells on Jan. 20 from its shoreline into waters near its disputed western sea border with South Korea, and the South Korean military returned warning shots from smaller weapons, reports the New York Times. Neither side reported casualties or damage. The North Korean military warned in a statement that more shells would be on their way as part of a winter training exercise, highlighting instability in the western waters. The rising tension at sea comes amid recent signals from Pyongyang that it was ready to return six-nation talks on ending its nuclear weapons program. In return for resuming the talks, North Korea has demanded talks on a peace treaty with the United States to formally end the 1950-3 Korean War and the lifting of United Nations sanctions tightened after its two nuclear tests. But the locations of the latest firing zones raised fears that North Korea might fire shells into South Korean-controlled waters to enforce a territorial claim, draw the South into dialogue and win economic concessions. In the past week the North threatened a “holy war to blow away” the Seoul government and the South warned that it would launch pre-emptive military strikes if it saw clear signs of an imminent nuclear attack from the North.