The Treasury Department said sanctions came into effect Monday against the Islamic Republic of Iran Shipping Lines, known by its acronym IRISL, as well as its Shanghai-based subsidiary E-Sail.

Under the sanctions, the United States threatens unilateral action against any government, business or person that does business with IRISL.

"We urge government authorities worldwide to investigate all IRISL and E-Sail activity in your ports and territorial seas and take appropriate action to put a halt to it," Secretary of State Mike Pompeo said in a statement.

"The world must be vigilant and take action to prevent Iran from acquiring proliferation-sensitive items that further threaten regional stability and security," he said.

IRISL, which has interests around the globe, is the world's 15th largest shipping line in terms of cargo carried, according to the latest figures available from database Alphaliner.

US officials say that IRISL has shipped sensitive cargo for Iran's military and assisted its ballistic missile program, which Tehran insists is legal as UN Security Council resolutions ban only nuclear-related activity.

IRISL was already under US sanctions related to Iran's nuclear program, but the latest move toughens the ramifications by targeting it more broadly over weapons of mass destruction.

The United States announced the sanctions in December but delayed their implementation, saying it wanted to give countries time to find other ways to conduct humanitarian trade not subject to US sanctions.

President Donald Trump imposed unilateral sanctions on Iran in 2018 when he walked out of a nuclear deal under which Tehran drastically scaled back its atomic activities in exchange for promises of economic relief.

China remains the primary trading partner of Iran, with US allies leaving the country due to the threat of US sanctions.