BEIJING (Reuters) -The responsibility of tackling the fentanyl issue in the United States lies within the U.S. itself, China's foreign ministry said on Tuesday, rejecting the punitive tariffs Washington imposed on Beijing for not stemming the inflow. China has repeatedly said fentanyl is a U.S. issue and the tariffs imposed on China because of that are unreasonable, said Lin Jian, a ministry spokesperson, when asked at a regular news conference if fentanyl would be discussed in future trade talks.