"Self-restraint, which is a choice, is all that separates armistice and war," Gen. Vincent K. Brooks, commander of the US Forces Korea and the allies' Combined Forces Command, said in a joint statement with Gen. Lee Sun-jin, chairman of the South's Joint Chiefs of Staff.

They called it the Combined Statement on Alliance Response to the North's test-firing of what it claims to be an intercontinental ballistic missile. Pyongyang asserted that the test was successful.

Brooks took note of the allies' decision to stage a joint ballistic missile exercise earlier in the day in a show of force against the North.

As it shows, he added, "We are able to change our choice when so ordered by our alliance's national leaders. It would be a grave mistake for anyone to believe anything to the contrary."

Lee said South Korea and the United States are maintaining "patience and self-restraint" despite the North's repeated provocations.

"As the combined live fire demonstrated, we may make resolute decisions any time, if the alliance commanders-in-chief order it.

Whoever thinks differently is making a serious misjudgment," he stressed.

South Korea and the United States staged a massive combined ballistic missile exercise Wednesday, sending a warning message to North Korea, the allies' militaries said, a day after the communist country claimed a successful long-range missile test.

They were referring to joint live-fire ballistic missile drills, involving South's Hyunmoo-2A and the US Eighth Army's ATACMS, held along the east coast of the peninsula.

The training was organized at the suggestion of South Korean President Moon Jae-in following the North's ICBM announcement Tuesday. US President Donald Trump approved the plan in an emergency consultation between their national security advisers. (Yonhap)