South Korean jets and navy ships have fired a barrage of guided missiles into the ocean during drills in a display of military power two days after North Korea test-launched its first intercontinental ballistic missile.
The North's ICBM launch, its most successful missile test to date, has stoked security concerns in Washington, Seoul and Tokyo as it showed the country could eventually perfect a reliable nuclear missile capable of reaching anywhere in the US.
Analysts said the missile tested on Tuesday could reach Alaska if launched at a normal trajectory.
The live-fire drills off South Korea's east coast were previously scheduled. In a show of force, South Korea and the US also staged "deep strike" precision missile firing drills on Wednesday as a warning to the North.
Thursday's drills were aimed at boosting readiness against possible North Korean maritime aggression. They involved 15 warships including a 3,200-ton destroyer, as well as helicopters and fighter jets, South Korea's navy said in a statement.
"Our military is maintaining the highest-level of readiness to make a swift response even if a war breaks out today," said Rear Admiral Kwon Jeong Seob, who directed the drills, according to the statement.
After the ICBM launch, North Korean leader Kim Jong Un said he would never put his weapons programmes up for negotiation unless the US abandoned its hostile policy towards the North.
His statement suggested he will order more missile and nuclear tests until his country develops a functioning ICBM that can place the entire US within its striking distance.
In a UN Security Council session on Wednesday, US ambassador Nikki Haley said the launch was "a clear and sharp military escalation" and America is prepared to use its "considerable military forces" to defend itself and its allies "if we must".
She said the US administration prefers "not to go in that direction", but to use its "great capabilities in the area of trade" to address "those who threaten us and ... those who supply the threats".
Speaking in Berlin before the G20 summit, South Korean President Moon Jae-in said the world should look at tougher sanctions against the North and insisted the problem must be solved peacefully.
The UN Security Council could impose additional sanctions on North Korea, but it is not clear they would stop it from pursuing its nuclear and missile programmes since the country is already under multiple rounds of UN sanctions for its previous weapon tests.