The U.S. Treasury Department on Thursday slapped sanctions on Iran's metals sector -- a move that comes a day after it also sanctioned the captains of five Iranian ships that delivered gasoline to the authoritarian Maduro regime in Venezuela and said it would seek "snap back" sanctions against Iran if the U.N. Security Council doesn't extend an arms embargo against the rogue Middle-Eastern state.

Treasury Secretary Steven Mnuchin said that the proceeds from the Iranian metal industry are going toward the Islamic regime's malign activities, rather than taking care of its citizens.

“The Iranian regime continues to use profits from metals manufacturers and foreign sales agents to fund destabilizing behavior around the world,” Mnuchin said in a statement. “The United States remains committed to isolating key sectors of the Iranian economy until the revenues from such sectors are refocused toward the welfare of the Iranian people.”

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POMPEO SAYS IF UN DOESN'T EXTEND ARMS EMBARGO ON IRAN, US WILL SEEK SANCTIONS

He added in a tweet: "The Iranian regime continues to prioritize the funding of terrorist groups over the needs of the Iranian people. @USTreasury took action today to further restrict revenues from a key Iranian sector."

The top targets of the Wednesday sanctions are companies associated with the Mobarakeh Steel Company, which according to the Treasury Department produces about one percent of Iran's GDP. It was slapped with sanctions in 2018.

Among those are Tara Steel Trading GmbH, which is based in Germany and in 2018 sold "nearly the equivalent of 60 million dollars" of "metals and metal ores in Europe." Three other companies in the United Arab Emirates, majority-owned by Mobarakeh, also were designated for sanctions. The same is the case for Metil Steel, a manufacturer and exporter based in Iran.

Three other Iranian-based metals manufacturers and one Chinese company that the Treasury Department says "knowingly transferred 300 metric tons of graphite to an Iranian entity" were also included in Wednesday's round of sanctions.

Tensions between the U.S. and Iran have increased under President Trump's administration. Trump campaigned on withdrawing from the Iran nuclear deal, which was a signature accomplishment of the Obama administration, and did so in 2018. The U.S. has aimed to impose significant economic pressure on Iran via sanctions and other limits with the goal of forcing the regime to change its behavior to avoid further economic pain.

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BOLTON CALLS US WITHDRAWL FROM URAN NUCLEAR DEAL 'MY HAPPIEST MOMENT' IN TRUMP ADMINISTRATION

One provision of that deal -- an arms embargo on Iran -- is set to expire in October and the United States is currently lobbying the United Nations Security Council to extend it. It's threatening to impose "snap back" sanctions if the council refuses.

"Without action, on the 18th of [October], Iran will be able to purchase advanced weapon systems and become the arms dealer of choice for terrorists and rogue regimes all throughout the world. This is unacceptable," Secretary of State Mike Pompeo said Wednesday.

He quoted former President Barack Obama and former Secretary of State John Kerry, who each made comments that if the U.S. was not satisfied with how the deal was working out, that it could unilaterally reimpose the sanctions that were previously on the Iranian regime.

Pompeo added: "The legal options in the Security Council are clear. Our great preference is to have a Council resolution that would extend the arms embargo, but we are determined to ensure that that arms embargo continues."

Meanwhile, Russia has cast doubt on the idea that the U.S., after pulling out of the nuclear deal, could reimpose those sanctions.

And S.A. Mousavi, the spokesman for the Iranian foreign ministry, has claimed that the U.S. pressure campaign has been a "miserable failure."

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"US desperate moves against Iranian individuals - like the one announced by @SecPompeo, aka the #SecretaryofHate – just signal the miserable failure of the so-called “max pressure”. Despite US pressure, #Iran & #Venezuela remain steadfast in countering unlawful American sanctions," he said in a Wednesday tweet.

But the U.S. says it's Iran that's acted unlawfully.

"Given that Iran has neither abided by current restrictions nor demonstrated a change in its threatening behavior, Special Representative Hook and Ambassador Craft called on Security Council members to extend the arms embargo," the State Department said in a statement Wednesday.

In recent years, Iran has attacked Saudi Arabia with drones; created a dangerous environment in the Strait of Hormuz by seizing oil tankers in international waters; sent a drone toward a U.S. warship; used captured U.S. sailors for propaganda; armed the Houthi rebels in Yemen; tripled its stockpile of enriched uranium and more.

Fox News' Bradford Betz contributed to this report.