ROUGH CUT (NO REPORTER NARRATION)br br North Korea fired more than 100 artillery rounds into South Korean waters as part of a drill on Monday, prompting the South to fire back, officials in Seoul said, but the exercise appeared to be more saber-rattling from Pyongyang rather than the start of a military standoff.br br During a press briefing at the Pentagon, U.S. Defense Secretary Chuck Hagel warned North Korea that these actions must stop.br br "The North Koreans have to stop these provocative actions. And we've been very clear on that. Obviously when I'm in China, that will be a subject that I will discuss with my counterpart in China," Hagel said.br br North Korea also accused the South of "gangster-like" behavior at the weekend by "abducting" one of its fishing boats and threatened to retaliate. The South said it had sent the boat back after it drifted into its waters.br br The North had flagged its intentions to conduct the exercise in response to U.N.