north korea s army has promised what it called a merciless response to any us provocation reflecting growing tension about the country s nuclear and weapons programmes. china has called for calm, saying it fears conflict could break out at any moment. it comes as the united states says a huge bomb, dropped on so called islamic state militants in afghanistan, was the right weapon against the right target . the us military insists it was a local, tactical decision others believe its principal aim was as a show of strength. our security correspondent frank gardner reports. a powerful armada , in the words of president trump. this is the us navy s carl vinson carrier battle group, equipped with 90 strike aircraft and other weapons and diverted to the seas off north korea. mr trump is hoping it will intimidate that country s isolated regime into abandoning any further nuclear tests or long range missile launches. china has warned of the imminent danger of a war being trigg