Seizure of the Hankuk Chemi

The Seizure of the Hankuk Chemi, a South Korean oil tanker, by Iran’s Islamic Revolutionary Guard Corps (IRGC) Navy took place on January 4, 2021. The IRGC Navy claimed in a statement that the ship was seized because of "environmental and chemical pollution concerns." The South Korean company which owns the tanker denied the claim of pollution.
Background.
On January 4, 2021, the IRGC Navy seized a South Korean oil tanker with the commercial name "Hankuk Chemi" (한국케미) for allegedly polluting the Persian Gulf. The ship had departed Saudi Arabia’s Al Jubail port for South Korea carrying 7,200 tons of chemicals, mostly methanol. The ship's 20 crew members included: five South Koreans, eleven members from Myanmar, two from Indonesia and two from Vietnam.
South Korea called for the release of the tanker on January 5. Iranian official Ali Rabiei rejected the request and denied that the seizure of the ship constituted "hostage-taking," claiming that the only hostage was $7 billion of Iranian assets held in South Korean banks that had been frozen following U.S sanctions on Iran. Several days later, on January 10, South Korea's Deputy Foreign Minister, Choi Jong Kan, met with Abbas Araghchi, Deputy Foreign Minister of Iran, to discuss the matter. Choi requested the timely release of the tanker and its crew and reportedly said that Seoul was intent on resolving the issue.
In February, South Korea reportedly agreed to release at least $1 billion in Iranian assets frozen in two Korean banks.
 Iran released the '"Hankuk Chemi"' on April 9th, 2021.