Launches come days after South Korea and the US wrapped up military drills Pyongyang sees as an invasion rehearsal.
“North Korea fired an unspecified ballistic missile toward the East Sea,” the US Joint Chiefs of Staff said on Monday, referring to the body of water also known as the Sea of Japan.
Japan’s Coast Guard, which confirmed the launches, said the objects appeared to have already fallen.
The launches come days after the US and South Korea wrapped up 11 days of so-called Freedom Shield joint military drills.
North Korea has long condemned joint US-South Korea military drills, calling them rehearsals for an invasion.
Pyongyang earlier this month warned that Seoul and Washington would pay a “dear price” for this year’s Freedom Shield drills, which involved twice as many troops as last year.
About 27,000 US soldiers are stationed in South Korea, where the drills took place.
North Korea’s test on Monday was the latest in a series of weapons demonstrations this year, including a missile tipped with a manoeuvrable hypersonic warhead on January 14.
Democracy Summit
Shortly after the missile launches, Blinken and South Korean President Yoon Suk-yeol took to the stage at the opening of the Summit for Democracy, which is this year being hosted by South Korea.
Both Blinken and Yoon spoke about how technology could be used to encourage democracy, but also to undermine it.
Blinken’s comments came after the US House of Representatives last week passed a bill that could see the popular social media app TikTok, which is owned by Chinese developer ByteDance, banned.
The democracy summit, an initiative of US President Joe Biden, has attracted criticism in past years due to its selective invitation list, with countries including Thailand and Turkey reportedly excluded.