South Korea's foreign minister on Tuesday dismissed reports that North Korea had shut down the Yongbyon nuclear power plant, which houses the country’s sole plutonium-producing nuclear reactor, according to a report by Yonhap News Agency.

“Many believe it is still in operation,” Yun Byung-se reportedly said, refuting claims by the Institute for Science and International Security, a Washington-based think tank.

A report released last week by the institute cited data gathered by U.S. satellites, which indicated that the 5-megawatt reactor had been shut down “possibly for either partial refueling or renovations.” The report, however, said that the precise reason for the possible shutdown was unknown.

“On whether the Yongbyon nuclear reactor has been shut down, and on the reasons for the shutdown if it is true, I do not necessarily have the same views as the report,” Yun reportedly said.

North Korea had, in 2005, pledged to abandon its nuclear program but it appeared to backtrack by testing devices in 2006, 2009 and 2013.

The country has also been conducting missile and nuclear tests since its negotiations with the South broke down in 2008. In recent month, however, its missile tests have intensified, apparently in response to a joint naval drill conducted in August by the United States and South Korea.

The South Korean foreign minister’s statements come just hours after North and South Korean ships exchanged warning shots near their disputed Yellow Sea border, which has been the site of frequent clashes between the two countries.

The incident also jeopardized planned high-level talks between the two countries, scheduled to take place in late October or early November.