In this March 17, 2020 photo, a shopkeeper wearing a face mask to help protect against the new coronavirus, waits for customers at the Tehran's Grand Bazaar, Iran. (VAHID SALEMI / AP)

WASHINGTON－The United States imposed fresh sanctions on Iran on Tuesday, keeping up its economic pressure campaign even as it offered to help Teheran cope with the coronavirus pandemic and called on the Islamic republic to release detained US citizens.

Iran is considering freeing some US citizens, US Secretary of State Mike Pompeo said at a news conference in which he made clear that Washington will maintain its maximum-pressure campaign to choke off Teheran's ability to export its oil.

Pompeo on Tuesday said his department is blacklisting nine foreign entities, as well as three Iranian individuals, for engaging in "significant transactions" to trade in Iranian petrochemical

The campaign, instituted after US President Donald Trump in 2018 unilaterally withdrew from a 2015 nuclear deal Iran struck with world powers, aims to force Iran to limit its nuclear, missile and regional activities.

Pompeo on Tuesday said his department is blacklisting nine foreign entities, as well as three Iranian individuals, for engaging in "significant transactions" to trade in Iranian petrochemicals.

While he did not name them, Pompeo said the step included blacklisting Iran's armed forces social security investment company and its director for investing in sanctioned entities.

Separately, the US Commerce Department said it will add six people－including five Iranian nuclear scientists－and 18 corporations to the US "Entity List" for aiding Iran's nuclear program, Pakistan's missile programs and Russian military modernization efforts.

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The Entity List names foreign parties that are barred from receiving some or all items subject to US export regulations unless the exporter secures a license, according to the department.

Unlikely to ease

On Monday, sources familiar with the matter who spoke on condition of anonymity because of the sensitivity of the issue said the US was unlikely to ease sanctions on Iran.

Pompeo urged Iran to free US citizens it has detained as a humanitarian gesture because of the coronavirus. Iran has reported 16,169 coronavirus cases and 988 deaths in one of the worst national outbreaks outside China, where the pandemic originated.

"We are aware that they are thinking about whether to release them or not," Pompeo told reporters. "We are urging them ... to release every American that is being wrongfully held there as a humanitarian gesture, given the risk that is posed."

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It is not clear exactly how many US citizens Iran may hold, but they include Michael White, a Navy veteran and possibly Robert Levinson, a former FBI agent.