North Korea appears to be readying for a possible third nuclear test as early as next March, a newspaper reported on Wednesday, as a U.S. politician travelled to Pyongyang with a message for the North to "calm down." US and South Korean intelligence have been watching the North's nuclear sites for any activity. Analysts say the North could use a test to try to gain leverage in international talks it is seeking and secure aid to prop up its destitute economy. South Korea's Chosun Ilbo daily on Wednesday cited an intelligence official from Seoul as saying a tunnel was being dug at the country's nuclear test site that could be completed in March next year, possibly heralding a new nuclear test.