Pentagon says it has secured an understanding with China that it will return an underwater drone seized in the South China Sea. China captured the US vessel in international waters on Thursday. <br/><br/>China has not explained why it captured the vessel and accused the US of hyping-up the incident. <br/><br/>US President-elect Donald Trump accused the Chinese of stealing the drone. The incident is among the most serious military confrontations between the two countries for decades.<br/><br/>Pentagon said the drone, known as an unmanned underwater vehicl was being used to carry out scientific research at the time it was captured and demanded its immediate return. It warned China not to repeat such a move in the future.