The United States issued a stern warning Tuesday that it was prepared to "defend ourselves and our allies" after North Korea test-fired a ballistic missile towards the Sea of Japan.

"We are aware of reports that the DPRK (North Korea) fired ballistic missiles," said State Department spokeswoman Anna Richey-Allen, noting that Washington strongly condemned this and other recent tests.

"We remain prepared to work with our allies and partners around the world to respond to further DPRK provocations, as well as to defend ourselves and our allies from any attack or provocation."

Richey-Allen said the US commitment to defending allies like South Korea and Japan remains "ironclad."

The United States plans to rally against Pyongyang's latest test at the United Nations.

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

Tuesday's test was an apparent show of force against the planned deployment of a US missile defence system and comes ahead of a US-South Korea joint military exercise scheduled for later this month.

Last week, North Korea's newly appointed foreign minister, Ri Yong-Ho, said any decision to conduct another nuclear test would depend on the behavior of the United States.

His comments came after top Washington envoy John Kerry warned the North of "real consequences" if it continues nuclear and missile tests in defiance of UN sanctions, as the international community attempts to rein in the rogue nation.

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 repeatedly warned of pre-emptive nuclear strikes against the South and US targets, although the main focus of its nuclear weapons program is to develop a credible strike threat against the US mainland.

The UN Security Council has slapped North Korea with its toughest sanctions to date in a unanimous decision even endorsed by China, its economic lifeline and diplomatic shield.