Iran's President Hassan Rouhani has ordered the head of the country's Atomic Energy Organization to start planning the development of nuclear-powered ships in reaction to what he called the United States' violation of their nuclear deal.
Earlier in December the US Senate voted to extend the Iran Sanctions Act by 10 years, a decision that was criticised by the Iranian foreign minister at the time who said it showed the US government had "a lack of credibility".
In a letter read out on state television, Mr Rouhani condemned the move as a breach of the 2015 nuclear accord and told the nation's scientists to begin "planning the design and production of fuel and nuclear power plants for maritime transport".
The leader also said he had ordered the foreign minister to mount a legal challenge against the US.
The 2015 nuclear accord between Iran and six world powers lifted a variety of sanctions against the nation in exchange for restrictions on the Iranian nuclear programme.
Yet the US keeps its own set of trade restrictions against the country, separate from the agreement, which were set to expire at the end of the year.
Politicians in the Senate said the sanctions were extended not only because of nuclear issues, but also over concerns about ballistic missile-testing and human rights in the country.
President Barack Obama is expected to sign the extension into law in the coming days.
The nuclear marine propulsion technology Iran has vowed to develop uses a nuclear reactor to generate electricity on a ship.
