has seized a second oil tanker it claims was involved in delivering fuel to .
Authorities are holding the Panama-registered vessel on suspicion it breached international sanctions that ban the supply of fuel to the communist state.
The tanker, named KOTI, and its crew are being held at the port of Pyeongtaek-Dangjin. Few details of the alleged illegal trading have been provided, but the vessel is believed to have been seized between 19 and 21 December.
The Yonhap news agency said the ship could store up to 5,100 tons of oil, and had a crew originating mostly from China and Myanmar.
It comes just days after South Korea announced it had seized a Hong Kong-registered tanker that it claimed had transferred around 600 tons of oil to a North Korean boat in international waters.
The vessel, named the Lighthouse Winmore, is accused of breaching UN sanctions (adopted in 2011) that ban ship-to-ship trading with North Korea. The tanker had been charted by a Taiwanese company.
Donald Trump subsequently claimed China was secretly helping to supply North Korea with oil.
The US President wrote on “Caught RED HANDED – very disappointed that China is allowing oil to go into North Korea.
“There will never be a friendly solution to the North Korea problem if this continues to happen!”
South Korean newspaper Chosun Ilbo claimed US intelligence agencies have used satellites to photograph Chinese ships transferring oil to North Korean vessels, on around 30 occasions.
China strongly denied the accusation, with a government spokesman saying the alleged transfers “absolutely do not exist”.
Reuters has reported that Russian ships have also transferred fuel to North Korea on several occasions.
Russia dismissed the suggestion, insisting it had “fully and strictly observed the sanctions regime”. There is no suggestion the activity had the backing of the Russian government.
Earlier this month the UN Security Council voted to further reduce the amount of oil that North Korea is allowed to import, and pledged to clamp down on ships illegally transferring fuel to the country.