The US Defence Secretary Ash Carter stated on Wednesday that the US military was guardedly keeping eye on North Korea's missile and nuclear programs.
Carter said the US was continuously taking measures, as it expands its defences, such as the number of ground-based missile interceptors in Alaska and Hawaii which were increased from 30 to 44 to guard against a potential missile attack by Pyongyang.
Meanwhile, South Korea and Japan urged North Korea on Wednesday to stop its controversial plan to conduct a long-range missile test.
South Korea warned Pyongyang that it would pay a "severe price" if it continues with its plan.
Japanese Prime Minister Shinzo Abe also said he would work together with the United States and other states to "strongly demand" that North Korea abstain from the plan.