The United States has sought to reassure China over joint US-South Korean military exercises, with the Pentagon insisting that the war games were not directed at Beijing. Pentagon spokesman Darryn James said as with previous exercises in this series, these operations were defencive in nature and designed to strengthen deterrence against North Korea.The four-day exercises starting on Sunday come in the wake of North Korea's artillery bombardment of a South Korean island, and will include a US aircraft carrier in a bid to deter the North. A Chinese Foreign Ministry spokesman told reporters on Thursday that Beijing was concerned over the action, saying China opposes any act that undermines peace and stability of the Korean peninsula.