South Korea launched a ballistic missile exercise early Monday in response to Pyongyang's provocative detonation of what it claimed was a miniaturised hydrogen bomb, state news agency Yonhap reported.
The South's military conducted a live-fire exercise simulating an attack on the North's nuclear site, hitting "designated targets in the East Sea", the report added, quoting the Joint Chiefs of Staff.
"The training came in response to the North's sixth nuclear test... and involved the country's Hyunmoo ballistic missile and the F-15K fighter jets," it said.
The South's military said the range to the simulated targets was equivalent to the North's Punggye-ri nuclear test site in its northeastern province.
US President Donald Trump Sunday criticised Seoul.
South Korea, Trump said, "is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"
The United States warned it could launch a "massive military response" to threats from North Korea.