TAIPEI, Taiwan — Prosecutors in Taiwan have accused a former judge and his son of violating United Nations sanctions on trade with North Korea, the second such case involving citizens of Taiwan so far this year. Both cases also involve Chinese nationals.

The Taipei District Prosecutors’ Office said in a statement on Monday that Chiang Kuo-hua, previously a High Court judge, and his son, Chiang Heng, chartered a cargo ship through a Chinese middleman, which they used to transport coal to Vietnam from North Korea last summer.

On Sunday, prosecutors and police officers raided the offices of a company Mr. Chiang founded, as well as the residences of Mr. Chiang and his son and two other men believed to have been involved in the coal shipment. All four men were questioned on Sunday and have been accused of assisting terrorists and forging documents.

Prosecutors have accused Mr. Chiang and his son of purchasing four tons of anthracite coal at the North Korean port of Nampo, which they then shipped to the Vietnamese port of Cam Pha. To avoid detection, the crew reportedly switched off the ship’s Automatic Identification System, a tracking device required of ships carrying a certain amount of tonnage.