North Korea may be trying to restart its plutonium production reactor for the first time in five months, satellite imagery suggests, according to United Press International.

Photos of the Yongbyon Nuclear Scientific Research Center taken between Dec. 24 and Jan. 11 show increased activity, which experts at the U.S.-Korea Institute, a Johns Hopkins' School of Advanced International Affairs think tank, consider a possible attempt to reactivate the facility.

The imagery apparently displays steam and melted snow, which could be a sign that the reactor is generating head, the BBC reported. The U.S.-Korea Institute recommended further monitoring of the site to see whether it was a cause for concern.

"It remains too soon to reach a definitive conclusion on this and also on whether that effort is moving forward or encountering problems," noted a report issued by the organization.

The analysis was prepared by 38 North, a North Korea monitoring project at the Washington think tank, Reuters detailed. It cautioned that there were clear differences between the latest photos and those from a year earlier, when the reactor was known to have been operating.

One possibility is that the North Koreans are in the early stages of an effort to restart the reactor after an almost five-month hiatus in operations, the report indicated. However, the facility has been recently observed over a period of only a few weeks," the researchers added.

Pyongyang had announced in April 2013 that it would revive the five-megawatt research reactor in an effort to expand its deterrent capacity. The move was condemned by the member states of the International Atomic Energy Agency, the United Nations' nuclear watchdog.

North Korea conducted underground nuclear tests in 2006, 2009 and 2013, United Press International noted, defying U.S. calls to show a commitment to denuclearize. South Korea's defense ministry on Thursday said that there was "no circumstantial report that North Korea is making final preparations for a test," the BBC added.

On a two-day visit to the South's capital, Seoul, the undersecretary of State for political affairs said the denuclearization of the Korean peninsula remained a priority for the United States.

"We look forward to ending the division and for the Korean people to be in a unified country under democratic rule without any nuclear weapons, without any threat to the territory," Wendy Sherman noted.