"North Korea's actions are dangerous and they're provocative," the White House spokesperson Jay Carney said at a regular news briefing. "And the DPRK's (North Korea) continued threats and provocations aggravate tensions and further North Korea's isolation."
He was responding to North Korea's artillery shells fired into South Korean waters in a live-fire drill on Monday, and to its threat to conduct a "new form" of nuclear test in response to continued US hostile policy, Xinhua reported.
US: We remain steadfast in our commitment to the defence of our allies
"We remain steadfast in our commitment to the defence of our allies," he added. "And any nuclear tests or any ballistic missile launches would be significant violations of U.N. Security Council resolutions."
South Korea's military fired back on the north with its K-9 self-propelled howitzers, and dispatched F-15K fighter jets to the sea border.
Tensions have escalated on the Korean Peninsula after Pyongyang fired a volley of short- and medium-range missiles in recent weeks.