North Korea likely breached an annual cap on oil imports set by the U.N. within the first five months of the year, employing obscure tankers for clandestine fuel delivery operations, according to a new U.N. report.

Twenty-five North Korean tankers made nearly 50 deliveries of refined oil products to Nampho Port and other facilities in the DPRK between Jan. 1 and May 1, according to analysis of satellite imagery provided by a member state to the U.N. Panel of Experts and published in its latest biannual report on North Korea sanctions violations.

North Korea “has