BEIJING -- With the USS Carl Vinson naval strike group heading for the Korean Peninsula, North Korea continues its show of defiance.

A statement released Sunday by the Pyongyang University of Science and Technology confirmed that Tony Kim, a U.S. citizen, had been detained “as he was about to leave” the country, after spending “several weeks” teaching at the school.

As CBS News correspondent Adriana Diaz reports, Kim, who also goes by the name Kim Sang-duk, is the third American now held in North Korea.

In 2016, Otto Warmbier, then a 21-year-old student from the University of Virginia, was sentenced to 15 years of hard labor in North Korea, for allegedly stealing a political banner from a Pyongyang hotel.

A few months later, Kim Dong Chul, a naturalized U.S. citizen, was sentenced to 10 years for espionage.

“This is typical North Korea at a time when there’s so much tension,” says former New Mexico Gov. Bill Richardson, who has negotiated previous prisoner releases with the North. “They use...these detainees from the United States as bargaining chips. They always want something in return.”

Since those arrests, the regime has continued its war of words, threatening Australia with a nuclear attack -- while Vice President Mike Pence was there -- for its alliance with the United States.

On Sunday, North Korean state-media took aim at the U.S. with rhetorical flourish, declaring its forces “combat-ready to sink a U.S. nuclear-powered aircraft carrier with a single strike.”

But Richardson says the arrest of another U.S. citizen may actually indicate there is still a “path forward,” as prisoner releases negotiated with the Kim regime in the past have “led to at least a dialogue with North Korea, and that’s a step forward.”

Because the United States has no diplomatic presence in North Korea, the State Department is working with the Swedish Embassy on Kim’s case. Kim’s wife was with him when he was arrested but was not detained, and is believed to still be in North Korea.

University officials said in their statement that Kim’s arrest is in no way related to his work at the school.

A South Korean news agency has reported Kim was engaged in relief and aid work in the North.