Top US general: North Korean nuclear attack is 'unimaginable' But Trump's chief strategist said there is no military solution for North Korea.

 -- The top U.S. general on Thursday warned that allowing North Korea to launch a nuclear attack on the United States would be "unimaginable."

Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, told reporters in Beijing that President Trump had asked military commanders to "develop credible viable military options" and "that's exactly what we're doing." But Dunford also called a military solution to the North Korean threat "horrific."

Dunford's comments came at the same time South Korean President Moon Jae-in said the U.S. has promised to seek its approval before taking military action against North Korea.

The U.S. has over 28,000 service members stationed in South Korea.

"I would consider that North Korea is crossing a red line if it launches an intercontinental ballistic missile again and weaponizes it by putting a nuclear warhead on top of the missile," Moon said Thursday.

Trump has promised "fire and fury" in response to recent North Korean threats. But his chief strategist Steve Bannon said in an interview published Wednesday night that there are no military solutions to the crisis on the Korean Peninsula.

“There’s no military solution, forget it," Bannon told The American Prospect. "Until somebody solves the part of the equation that shows me that 10 million people in Seoul don’t die in the first 30 minutes from conventional weapons, I don’t know what you’re talking about, there’s no military solution here, they got us.”

North Korea's leader Kim Jong Un threatened to launch missiles into the waters off of Guam last week. Guam is a U.S. island territory and hosts two U.S. military bases.

However, after reviewing the plans, Kim seemed to walk back his threat, saying he would wait and observe the "foolish and stupid conduct of the Yankees."

North Korea tested its second intercontinental ballistic missile in late July.

Dunford's comments to reporters followed a nearly week-long trip to Asia, which included stops in South Korea and China.

Earlier in the week, Dunford and his Chinese counterparts signed an agreement designed to "improve communication between their militaries and reduce the chances of miscalculations." A direct line of communication at the three-star level would also be established.

U.S.-Chinese communications are especially crucial as "the region and world are facing the dangers of a nuclear-armed North Korea," according to a Joint Staff press release.