North Korea has carried out a successful ground test of a new rocket engine to launch satellites. Kim Jong-un, the country's leader, asked scientists and engineers to make preparations for a satellite launch as soon as possible. It is the latest in a series of missile-related tests this year. Meanwhile, the US and China have agreed to step up co-operation at the UN to address the North's fifth nuclear test. <br/><br/>The underground nuclear test, conducted earlier this month, is thought to be the country's most powerful yet. North Korea regularly makes claims about the progress of its nuclear and missile programmes, but analysts say most of them are impossible to independently verify.<br/><br/>According to Diplomats, US and Chinese officials have started discussions on a possible UN sanctions resolution as a response. But Beijing has not said directly whether it will support tougher steps against Pyongyang.