Chinese President Xi Jinping offered North Korean leader Kim Jong-un firm backing in deadlocked nuclear talks with the United States (US) and reasserted Beijing's key role in the wider process, according to the two allies' state media Thursday.Kim visited Beijing by train this week for two days of talks with Xi seen as a strategy session ahead of a second summit between the North Korean leader and US President Donald Trump.At their first meeting in Singapore in June, Kim and Trump s