North Korea has reportedly test-fired two medium-range Musudan ballistic missiles from Wonsan, a port city on the country's eastern coast.
The missiles violate the UN Security Council resolution, which prohibits North Korea's use of ballistic missile technology, according to US Pacific Command spokesperson commander Dave Benham.
US State Department spokesman John Kirby was quoted by the BBC as saying: "We intend to raise our concerns at the UN to bolster international resolve in holding [North Korea] accountable for these provocative actions."
US and South Korean officials said that the first launch was considered a failure, with the missile travelling more than 150km before landing in the sea.
During the second trial, the missile flew 400km and the data is currently being analysed by the South Korean military, CNN reported.
The North American Aerospace Defense Command (NORAD) found that the missiles did not pose a threat to North America.
Kirby said that the tests would provoke the US to increase its efforts to stop North Korea's weapons programme, according to BBC.
The back-to-back launches are the latest in a series of failed missile launches by North Korea.
With a range of more than 3,000km, the Musudan missiles would be able to hit South Korea and Japan, as well as US military bases on Guam.