Washington/ Tokyo: The US on Tuesday strongly condemned North Korea's "provocative" ballistic missile 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 (DPRK) 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 UN 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.

"We intend to raise our concerns at the UN to bolster international resolve in holding the DPRK accountable for these provocative actions," Mason said.

America's commitment to the defence of its allies, including South Korea and Japan, in the face of these threats, remains "iron-clad", she said.

The US remains prepared to work with its allies and partners around the world to respond to further North Korean provocations as well as to defend itself and allies from any attack or provocation, Mason said.

"We call on North Korea to refrain from actions and rhetoric that further raise tensions in the region and to focus instead on taking concrete steps toward fulfilling its commitments and international obligations and commitments," Mason said.

According to the US Strategic Command, its systems detected two North Korean missile launches on August 2, 2016.

"The simultaneous launch of two presumed No Dong intermediate range ballistic missiles occurred near the western city of Hwangju," it said.

"Initial indications reveal one of the missiles exploded immediately after launch, while the second was tracked over North Korea and into the Sea of Japan," US Strategic Command said in a statement.

The North American Aerospace Defense Command (NORAD) determined the missile launches from North Korea did not pose a threat to North America.

Japan Prime Minister Shinzo Abe also condemned the North Korean 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."

Defence minister Gen Nakatani said the missile landed in the Sea of Japan off the north coast in the country's Exclusive Economic Zone (EEZ) - the first time a North Korean missile has landed in Japan's EEZ since 1998.

It was the first ever North Korean missile to land in Japan's EEZ in the Sea of Japan (East Sea) facing the Korean peninsula. The North Korean missile in 1998 landed in Japan's EEZ in the Pacific Ocean after having flown over the country's territory.

Chief cabinet secretary Yoshihide Suga, the government's top spokesman, also harshly criticised the launch.

"There was no early warning," he told reporters. "From the perspective of the safety of aircraft and ships, it is an extremely problematic, dangerous act," he added.

"We immediately launched a strong protest against North Korea and condemned (the launch) in the strongest language" through diplomatic channels, he said.