(CNN) -- An American was detained in North Korea for trespassing on the country's border with China, the state-run news agency reported Thursday.
The unidentified person was detained on Monday, and the incident is under investigation, according to a report by Korea Central News Agency.
U.S. State Department spokesman P.J. Crowley said Thursday afternoon that the department had been able to get no information on the reported incident.
"At this point we take the report very seriously," he said at his afternoon briefing in Washington. "We have looked into it. Have we got confirmation yet? No."
North Korea announced on December 29 that it was holding an American who had entered the country illegally from China on Christmas Eve. KCNA did not identify the man, who it said was "now under investigation by a relevant organ."
At the time, U.S. State Department spokesman Ian Kelly said Washington was concerned by reports that a Korean-American missionary, Robert Park, had gone into North Korea, but could not confirm them.
Washington and Pyongyang have no diplomatic relations. The United States relies on the Swedish Embassy to look after U.S. interests in North Korea.
"Right now we are operating on the assumption that it is entirely possible we have a second American citizen detained in North Korea, in addition to Robert Park," Crowley said. "On Mr. Park we continue to seek consular access to him through our protecting power in Pyongyang, and I must say if this report is verified we would seek the same access to a second American citizen, should that be the case."
Park told relatives before Christmas that he was trying to sneak into the isolated communist state to bring a message of "Christ's love and forgiveness" to North Korean leader Kim Jong Il. In a written statement issued on the family's behalf, his brother, Paul Park, said in late December that Park's well-being "has been a source of ongoing concern and anxiety" since they received reports that he had entered North Korea.
North Korean authorities take a dim view of people who enter the country without authorization. Two American journalists who were arrested along the North Korean-Chinese border in March faced a 12-year sentence of hard labor, but were released after a meeting between Kim and former U.S. President Bill Clinton in Pyongyang.
But Park's parents told CNN affiliate KFMB in December that their son was willing to risk his life to deliver his message to Kim.
Detention of Park, and now possibly another American, adds to already strained and complicated relations between the United States and North Korea.
The United States has recently criticized as "provocative" North Korea's declaration of a "no-sail" area off its western border with South Korea and its firing artillery along that sea border.
And the United States continues to ask North Korea to return to talks about ending its nuclear program. The six-party talks involve North and South Korea, the United States, Russia, Japan and China.
"As to what North Korea's intentions may be at any particular time, who knows?" Crowley said Thursday, raising his hands in the air.
"We have seen provocative actions in the past. We always have concerns about this," he said. "We don't know what they are thinking. We know what they should be doing, which is return to the six-party process."