South Korea's defence ministry said on Monday the five-day drill called Vigilant Ace will improve their capabilities in wartime.
The US 7th Air Force deployed major strategic military assets including six F-22 and 18 F-35 stealth fighter jets for the regular exercise in the Korean Peninsula.
About 12 000 US military personnel are participating.
It takes places a week after North Korea test-launched its most powerful intercontinental ballistic missile that puts most of the US within range.
On Sunday, Senator Lindsey Graham said it is time for US military families in South Korea to leave the country because the conflict with North Korea is getting close.
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