The United States strongly condemned the test and asserted that America's commitment to the defence of its allies, including South Korea and Japan, in the face of such threats remains "iron-clad".
"We are aware of reports that the Democratic People's Republic of Korea fired ballistic missiles. We are monitoring and continuing to assess the situation in close coordination with our regional allies and partners," State Department spokeswoman Julia Mason said.
"We strongly condemn this and North Korea's other recent missile tests, which violate multiple United Nations Security Council Resolutions explicitly prohibiting North Korea's launches using ballistic missile technology," Mason said.
These provocations only serve to increase the international community's resolve to counter the North Korean prohibited activities, including through implementing existing UN Security Council sanctions.
The latest test also comes amid mounting tensions ahead of a planned US-South Korea joint military exercise later this month. Last year the drills involved 30,000 US soldiers and 50,000 South Korean troops.
The missile was launched from near the western North Korea city of Unyul at around 07:50 am, South Korea's defence ministry said.
The projectile flew some 1,000 kilometres (621 miles) and was believed to be a Rodong mid-range missile, the defence ministry added.
Japanese Prime Minister Shinzo Abe has condemned the test missile that landed 250 kilometres (155 miles) off Japan's coast as an "outrageous act" which threatened his country.
"It's a serious threat against our country's security," Abe told reporters. "This is an outrageous act that cannot be tolerated."
The test follows the launch of three ballistic missiles on July 19 in what the North said were simulated nuclear strikes on the South.
Pyongyang has carried out a series of missile tests this year in defiance of tough UN sanctions, and vowed to take "physical action" against the planned deployment of a US missile defence system in the South announced in July.
Since leader Kim Jong-Un took over from his late father Kim Jong-Il, who died in 2011, North Korea is believed to have tested 16 Scud missiles with a range of between 300 km and 1,000 km, six Rodong missiles, six Musudan missiles with a range of up to 4,000 km and three submarine-launched missiles, according to the South's Yonhap news agency.
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