Secretary of State Mike Pompeo announced Thursday that the U.S. has imposed additional sanctions on Iran’s metal exports that supply revenue for the country’s Revolutionary Guard Corps.

Eight companies in Iran were designated as businesses working in the iron, steel and aluminum sectors affiliated with the Mobarakeh Steel Company -- which had previously been placed under U.S. sanctions.

The U.S. also placed sanctions on a Chinese company based out of Hong Kong, known as the Global Industrial and Engineering Supply Ltd., for providing graphite -- a vital material in Iran’s metal industry -- to Tehran in 2019.

“As part of our maximum pressure campaign, the United States designated eight entities connected with Iran’s metal industry and designated an entity that transferred material to Iran that is critical to Tehran’s metal plants,” Pompeo said in a statement.

The Revolutionary Guard is a branch of the Iranian armed forces and was designated a terrorist organization by President Trump in April 2019.

Iran reportedly uses the funds it receives from the exports of its metal industry to provide funding for the Revolutionary Guard.

“Any person doing business with [Revolutionary Guard] or conducting prohibited transfers of graphite to Iran risks sanctions,” Pompeo said.

The companies have also been added to the list of “blocked persons,” preventing them from entering the U.S.

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The U.S. has imposed strict sanctions on Iran since President Trump pulled out of the Iranian nuclear deal in 2018, calling the Obama-era agreement “decaying and rotten.”

Pompeo on Tuesday also urged the United Nations Security Council to indefinitely extend the arms embargo on Iran, which is set to expire in October.

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Iran faced additional criticism from the International Atomic Energy Agency (IAEA) last week after the group signed a resolution condemning Iran’s transparency and obligations regarding its nuclear program.

IAEA Director-General Rafael Grossi accused Iran of preventing foreign investigators from gaining access to various nuclear sites, a violation of Iran’s contractual safeguard obligations.

China, which has had strained relations with the U.S. over the last few months, has condemned the IAEA resolution and has said it will not support extending the arms embargo.

As U.S. relations with Tehran worsen, China and Iran are building stronger ties, according to Iranian Foreign Minister Mohammad Javad Zarif, who said in a Tweet Tuesday that they “reached consensus on deepening the comprehensive strategic partnership between the two countries.”

“We all reaffirm our support for the Iranian nuclear agreement, multilateralism and international law, and jointly oppose unilateralism and the weakening of the Iranian nuclear agreement,” Zarif said.

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The newest round of sanctions is the latest attempt by the U.S. to prevent Iran from developing its nuclear capabilities, a strategy that some security experts have said will further destabilize nuclear non-proliferation in the Middle East and potentially globally.

“Today’s important actions block the property and interests…of these sanctioned entities and deny them access to the U.S. financial system,” Pompeo said. “We will continue to exert maximum pressure on Iran until the regime decides to start behaving like a normal country.”