As North Korea ratchets up its hostile rhetoric, announcing Thursday that its military has been cleared to attack the United States with nuclear weapons and that "the moment of explosion is approaching fast," international lawyers are debating whether the United States would have legal justification to launch a pre-emptive strike.

While lawyers agree it’s still highly unlikely that the U.S.military would strike the first blow, some said such an attack could be justified under international law if North Korea is deemed an imminent threat.

"Rhetoric alone does not pose an imminent threat," said Arnold & Porter partner John Bellinger III, who served as the State Department’s top lawyer from 2005 to 2009 and the National Security Council’s legal adviser from 2001 to 2005. "But if the U.S. felt that North Korea did pose an imminent threat of attack, certainly U.S. government lawyers would conclude that the government has the right to act under the age-old doctrine of anticipatory self-defense."

Others disagree. "The idea that there is any right of pre-emptive self-defense is erroneous," said Mary Ellen O’Connell, a professor at University of Notre Dame The Law School who specializes in international law on the use of force

Under the United Nations Charter, use of force against another country is legal in just two circumstances: in self-defense "if an armed attack occurs," or by authorization of the Security Council.

This means an armed attack must actually be underway, O’Connell said, adding that could include, for example, satellite photos showing weapons being readied to launch. "It’s an emergency right of self-defense when you’re really coming under attack."

The notion of pre-emptive self-defense was revamped during the George W. Bush administration in the months preceding the invasion of Iraq in March 2003.

In November 2002, William Taft IV—at the time the State Department’s top lawyer, now of counsel at Fried, Frank, Harris, Shriver & Jacobson—wrote in a memo:"In the face of overwhelming evidence of an imminent threat, a nation may take preemptive action to defend its nationals from unimaginable harm."

Taft continued, "The United States reserves the right to use force preemptively in self-defense when faced with an imminent threat. While the definition of imminent must recognize the threat posed by weapons of mass destruction and the intentions of those who possess them, the decision to undertake any action must meet the test of necessity."

In Iraq, imminent threat included the possibility that Saddam Hussein’s regime possessed weapons of mass destruction and had in the past used them against others.

The question is, is North Korea an imminent threat?

In recent days, that country has issued a series of belligerent statements, declaring it was in "a state of war" with South Korea and that its military has been authorized to use "smaller, lighter and diversified nuclear" weapons to counter U.S. "aggression."

There have been actions as well. South Korea on Thursday reported its northern neighbor moved a missile "with considerable range" to its coast. North Korea last week released a photograph of Kim Jong-un in an emergency military meeting with a chart labeled "U.S. mainland strike plan" in the background. The chart shows missile trajectories hitting Washington, Los Angeles, Hawaii and Austin, Texas.

"Some of the actions they’ve taken over the last few weeks present a real and clear danger and threat to the interests certainly of our allies, starting with South Korea and Japan and also the threats that the North Koreans have leveled directly at the United States," Defense Secretary Chuck Hagel said in a speech on Wednesday.

But O’Connell stressed that none of this rises to the level that self-defense could justify an attack. "The actual law says ‘If an armed attack occurs.’ Otherwise, you have to go to the Security Council."

Bellinger counters that isn’t necessarily the case.

"The combination of rhetorical threat coupled with knowledge gained through intelligence…that North Korea has developed the capacity to hit the U.S. and has the intention to act" would be sufficient grounds to strike, Bellinger said. The only issue is "how ‘imminent’ does ‘imminent’ have to be when you’re talking about terrorists or being hit with a nuclear weapon."

Jenna Greene can be contacted at jgreene@alm.com.