In a move likely to increase tensions during President Trump's final weeks in office, Iranian semi-official media are reporting Tehran is enriching nuclear fuel to 20% purity. Separately, Iran seized a South Korean oil tanker in the Persian Gulf, South Korea's Foreign Ministry said Monday.
Iran accused the South Korean-flagged tanker Hankuk Chemi of oil pollution offenses. Iran's Tasnim News Agency published pictures described as showing Iran's Revolutionary Guards Corps speedboats escorting the tanker, which is reportedly being held at the port city of Bandar Abbas.
The seizure comes as South Korea's deputy foreign minister was expected to visit the Iranian capital to discuss billions of dollars in funds frozen in South Korean banks because of U.S. sanctions.
The Trump administration reimposed the sanctions in 2018, after the White House pulled the U.S. out of the 2015 nuclear agreement between Iran and six world powers.
On Monday, Iran also declared that it had begun enriching uranium up to 20% at its underground Fordow nuclear facility, which breaches limits in the nuclear accord.
Government spokesman Ali Rabiei told Iranian media that the process to produce UF6 enriched uranium was underway, after Iranian President Hassan Rouhani issued the order to proceed.
Twenty percent enriched uranium can be used in the production of medical isotopes. The next step would be 90%, which is weapons-grade uranium.
Under the nuclear deal, Iran was limited to enriching fuel to around 4% purity.
Iran has long denied seeking a nuclear weapon, and inspectors from the International Atomic Energy Agency have for years verified the peaceful nature of Iran's nuclear program. The IAEA now says it will be informing member states about Iran's latest moves.
But as tensions between Tehran and Washington spiked a year after a U.S. drone strike killed top Iranian Gen. Qassem Soleimani, Iranian lawmakers passed a bill calling for the higher level of enrichment.
Tehran is demanding that U.S. President-elect Joe Biden rejoin the nuclear agreement and once again lift sanctions on Iran. U.S. officials have suggested that Washington would also seek new provisions, such as limits on Iran's ballistic missile program.
Meanwhile, Iranian media are reporting the crew of the seized South Korean oil tanker are under arrest.