North Korea nuclear test: South holds live-fire missile drill

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. 
The live-fire exercise saw ballistic missiles launched from fighter jets and the ground.  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".  The North says 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.  In the past two months it has conducted intercontinental ballistic missile tests, sending one over mainland Japan into the Pacific Ocean. It has also threatened to send missiles towards the US Pacific territory of Guam.  The UN Security Council is to hold an emergency meeting on Monday to discuss its response.