China's nuclear envoy in South Korea amid talk of Trump action against North Korea

The aircraft carrier USS Carl Vinson (CVN 70) transits the South China Sea, April 8, 2017. U.S. Navy photo by Mass Communication Specialist 3rd Class Matt Brown/Handout via Reuters

SEOUL/TOKYO (Reuters) - China and South Korea agreed on Monday to slap tougher sanctions on North Korea if it carries out nuclear or long-range missile tests, a senior official in Seoul said, as a U.S. Navy strike group headed to the region in a show of force.

North Korea marks several major anniversaries this month and often marks the occasions with major tests of military hardware.