North Korea acknowledged it detained an American for illegally entering the reclusive country, news welcomed by relatives of an Arizona missionary who feared they would never hear from him again after he sneaked across the border.

Activists say they last saw Robert Park as he slipped across the frozen Tumen River into North Korea on Christmas Day, carrying letters urging the country's absolute leader to step down and free the hundreds of thousands of people held in political camps.

After four days without any word, relatives of the 28-year-old Korean-American said Tuesday they were relieved when the communist country finally announced it had a U.S. citizen in custody — though analysts say Park's actions are likely to be seen as hostile to the regime and could draw a long prison sentence.

"My fear was that they say they don't know anything about it and may get rid of him secretly," Manchul Cho, an uncle of Park, told The Associated Press in California. "Once they recognize it, that's really good."

The two-sentence dispatch from the official Korean Central News Agency said an American was being investigated after "illegally entering" the country on Christmas Eve. The report did not identify the man, but activists and family believe it is Park. There was no immediate explanation for the discrepancy in the date of entry.

In Washington, U.S. State Department spokesman Ian Kelly said that North Korea had "confirmed it is holding a U.S. citizen pending an investigation," and that the U.S., which does not have diplomatic ties with Pyongyang, would seek consular access to the citizen through the Swedish Embassy.

Cho, a Los Angeles psychiatrist, said he hopes North Korea will deport Park, a devout Christian, noting that a long incarceration would only galvanize critics of the communist regime.

The Rev. Madison Shockley, a Park family pastor in Carlsbad, California, also called the announcement positive news.

"Without acknowledging his presence, they could do anything and we'd never hear from him again. They could have said 'we don't know who you're talking about,"' he said. "Now, by acknowledging, they have accountability for it."

Just months ago, North Korea freed two U.S. journalists arrested in March whom it had sentenced to 12 years of hard labor for trespassing and engaging in "hostile acts." The women were released in August to former U.S. President Bill Clinton, who journeyed to Pyongyang to negotiate their freedom.

The latest detention could give the North bargaining power with Washington, which is trying to coax Pyongyang to return to the international talks aimed at ending its nuclear weapons programs. The two countries agreed on the need to resume the negotiations during a trip to Pyongyang by President Barack Obama's special envoy earlier this month, but North Korea did not make a firm commitment on when it would rejoin the talks.

Analysts have suggested that the negotiations to free American reporters Euna Lee and Laura Ling may have been a turning point for U.S.-North Korea relations, giving the volatile regime the opportunity to make a fresh start with Washington.

Now, Pyongyang finds itself once again holding a trump card.

Park's detention presents "a diplomatic headache for the two countries," said Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University, adding that the North could try to take advantage of the detention issue in its negotiations with the U.S.

But he said Washington is unlikely to go to the same lengths for Park as it did in the high-profile detention of Ling and Lee, who work for the Current TV media venture started by former U.S. Vice President Al Gore.

North Korea's criminal code punishes illegal entry with up to three years in prison, but it's unclear how the North might handle Park's case.

Analyst Paik Hak-soon of the private Sejong Institute think tank in South Korea predicted Pyongyang will sentence Park to a lengthy prison term, then free him.

The Rev. John Benson, pastor at Life in Christ Community Church in Park's hometown of Tucson, Arizona, supported Park's self-proclaimed mission to draw attention to the situation in North Korea.

"Drastic situations call for drastic measures. We all need to wake up and not pay lip service to North Korea," Benson said. "We need to take action, and that is what Robert is doing."

North Korea holds some 154,000 political prisoners in six large camps across the country, according to South Korean government estimates. Pyongyang has long been regarded as having one of the world's worst human rights records, but it denies the existence of prison camps.