An obscure Sierra Leone-flagged freighter with a murky past appeared in key North Korean ports in what experts described as a possible attempt to smuggle energy resources or weaponry in violation of U.N. sanctions.

The 1,361-ton Valiant sailed from Kaohsiung, Taiwan, on Sept. 28 and reached North Korea’s largest port of Nampho on Sept. 30 and Songnim — a DPRK port upstream of the Taedong River — on Oct. 4, Marine Traffic data shows.