North Korean leader Kim Jong Un visited a uranium enrichment plant and said boosting nuclear weapons production is necessary to deter enemy attacks, according to state media on Wednesday.

“The external environment we face remains severe and that the challenges posed by hostile forces seeking to establish military superiority are becoming even more intense,” he said in the Rodong Sinmun report, using the common code word “hostile forces” to refer indirectly to the U.S., South Korea and Japan.

The apparent warning to Washington comes after newly inaugurated President Donald Trump declared North Korea a “nuclear power” and expressed interest