South Korea has conducted a missile drill simulating an attack on the North Korean nuclear test site, in response to Pyongyang's sixth nuclear test. Quoting the Joint Chiefs of Staff state news agency Yonhap reported that the military conducted a live-fire exercise late yesterday simulating an attack on the North's nuclear site, hitting designated targets in the East Sea.<br/> <br/>The live-fire exercise saw ballistic missiles launched from fighter jets and the ground. The South Korea's military said the range to the simulated targets were equivalent to the North's Punggye-ri nuclear test site in its northeastern province. It came as US defence chief James Mattis warned that any threat to the US or its allies by Pyongyang would be met with a "massive military response".<br/> <br/>North Korea has said it tested a hydrogen bomb that can fit a long-range missile. Pyongyang has repeatedly defied UN sanctions and international pressure by developing nuclear weapons and testing missiles, and the provocations have only intensified. The UN Security Council is to hold an emergency meeting today to discuss its response.