WASHINGTON - The United States will work with the United Nations Security Council on 'significant measures' to hold North Korea to account for its launching of a rocket, US Secretary of State John Kerry said on Saturday. Calling the launch 'a flagrant violation' of UN resolutions on the country's use of ballistic missile technology, Kerry in a statement reaffirmed the 'ironclad' US defense commitments to Japan and South Korea and called the launch a 'destabilizing and unacceptable challenge' to peace and security.