The joint drills near the Korean Peninsula included US B-52 bombers and F-22 stealth fighter jets, besides F-35 and F-15 fighter jets from South Korea.
The two missiles flew some 500 kilometres and reached a maximum altitude of around 550 kilometres before landing in the Sea of Japan.
North Korean leader Kim Jong-un said last year that developing solid-fuel engines for more advanced missiles was a strategic priority.
Kim Jong-un says his country's ultimate goal is to "possess the world's most powerful strategic force" as he promotes scientists and officers behind recent test of "monster missile."
Kim Yo-jong accused South Korean President Yoon Suk-yeol of creating a "dangerous situation" after Seoul said that it was reviewing additional sanctions on North Korea over its recent barrage of missile tests.
If the US continues to make threats, Pyongyang "will resolutely react to nukes with nuclear weapons and to total confrontation with all-out confrontation," state media quotes leader Kim Jong-un as saying.
North Korea fires about a dozen missiles, including one that lands close to South Korea's territorial waters, prompting Seoul to issue a rare warning for people on an island and fire three missiles in response.
There were no reports of clashes between the Koreas.
Pyongyang test-fires a pair of long-range strategic missiles, with leader Kim Jong-un hailing another successful display of the country's tactical nuclear strike capability, state media report.
Leader Kim Jong-un guided exercises by nuclear tactical operation units over the past two weeks, involving ballistic missiles with mock nuclear warheads, state media said.
Leader Kim Jong-un says his country will never abandon nuclear weapons as parliament enacts a law authorising Pyongyang to "automatically" execute preventive nuclear strikes against enemy forces.
"No one barters its destiny for corn cake," says Kim Yo-jong, powerful sister of leader Kim Jong-un, responding to Seoul's offer to boost Pyongyang's economy in exchange for giving up nuclear weapons.
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