Rep. Joe Sestak (D-Pa.) said Friday that the U.S. military presence in the wake of North Korea attacking its southern neighbor is as much about deterring Pyongyang as it is encouraging South Korea to show "restraint."

Sestak, a member of the Armed Services Committee and a retired three-star admiral, said that the key to reining in North Korea is China.

"China wants to move into the international role of a -- of a rational actor in the international scene, but it's got an ally in North Korea that continues to do strange things," Sestak said on MSNBC.

"How well it helps move that to a less provocative stance is an indication if China really does want to move into the international arena as a rational player, particularly as other Asian nations watch it to see how closely they want to be working with China itself," he added.

North Korea warned Friday that U.S.-South Korean plans for military maneuvers put the peninsula on the brink of war, and the country fired fresh artillery rounds as the U.S. commander in the region surveyed the destruction on Yeonpyeong Island, which was struck by a barrage of North artillery fire on Tuesday.

Two South Korean servicemen and two civilians were killed in Tuesday's attack. Friday's fire struck nothing in South Korea, according to wire reports.

Sestak brushed off the "brink of war" warning as "normal talk by North Korea."

Sestak said that doesn't mean the situation can't spiral out of control. "And that's why when you heard President Lee of South Korea say, another strike by North Korea would mean he might have to strike bases of North Korea, this is why this movement of forces is as much, I believe, to restrain South Korea from unnecessary actions as it is to make sure who's really at fault here, North Korea, is told hold off as we work with China diplomatically," he said. "That's the key, is China."

He said the key is to "have a show of force, but don't be overly provocative. This is a delicate matter right now. I think we'll handle it well. But again, diplomacy has to prevail."

Sestak cautioned that the U.S. forces would be in the narrow Yellow Sea where North Korea sank the South Korean warship Cheonan last spring. "I commanded the USS George Washington aircraft carrier battle group," he said. "There's not a question that they are well trained and that they are making sure that the rules of engagement, if something happens at sea, that they know what the proper response is, that they don't overreact."