Radio Free Asia(RFA) says the U.S. Coast Guard has been keeping watch on more than 200 vessels related to North Korea since last month. 

Coast Guard Spokeswoman Alana Miller told RFA on Tuesday that pursuant to the Countering America's Adversaries Through Sanctions Act, the Coast Guard placed all North Korean ships under sanctions and surveillance. Miller said the Coast Guard posted a related statement on the Federal Register on February eighth. 

According to RFA, the Coast Guard is monitoring all ships weighing more than 300 tons which are suspected of having ties with North Korea. It quoted Miller as saying that the State Department has drawn up a list of ships subject to surveillance and unveils an updated sanctions list online every month. 

RFA said that as of last Tuesday, 218 ships related to North Korea were on the list. Out of that total, the State Department and the Coast Guard have identified 198 to be North Korean ships.