China expressed its opposition on Thursday to unilateral sanctions against North Korea saying they could raise tension, after the United States imposed new curbs on the isolated country in retaliation for its nuclear and rocket tests. U.S. President Barack Obama on Wednesday imposed sweeping new sanctions on North Korea intended to further isolate its leadership after recent actions seen by the United States and its allies as provocative. The new sanctions threaten to ban from the global financial system anyone who does business with broad swaths of North Korea's economy, including its financial, mining and transport sectors.