The warnings about Iran and Russia came less than two weeks before the election between President Donald Trump and former Vice President Joe Biden.
Iran will more easily be able to sell weapons to its proxies, analysts say, including Lebanon's Hezbollah and the Houthi rebels in Yemen.
Schools, mosques, shops, restaurants and other public institutions in Tehran, where the infection rate has been highest, have been closed since Oct. 3.
The rial's nosedive comes as new sanctions from the Trump administration, enacted last Thursday, came down on 18 major Iranian banks.
While our "maximum economic pressure" campaign on Iran stays, peace and diplomacy "remains on the table" anytime the regime and Iran want to take us up on it, says Morgan Ortagus, a spokeswoman of the U.S. State Department.
"Our maximum economic pressure campaign remains but remember, President Trump has said that he wants a peaceful resolution with Iran," said Morgan Ortagus, spokeswoman of the U.S. State Department.
Secretary of State Mike Pompeo, flanked by Defense Secretary Mark Esper, Treasury Secretary Steven Mnuchin and Commerce Secretary Wilbur Ross, said the administration would sanction Iran's Ministry of Defense and Venezuela's Nicolas Maduro.
The announcement comes as the presidential campaigns are now pushing into the final two months of the race, NBC News reports.
U.S. President Donald Trump's campaign on Iran has been "cruel and counterproductive," with "very, very punishing sanctions that have not achieved any realistic goal," says Barbara Slavin, director of the Future of Iran Initiative at the Atlantic Council.
Secretary of State Mike Pompeo, who addressed the 15 member nations of the U.N. Security Council on Thursday, reiterated that the Trump administration will continue its maximum pressure campaign in order to rein in Tehran.
U.S. President Donald Trump wants to put more pressure on Iran, while Democratic presidential candidate Joe Biden wants more engagement with the Isalmic Republic, said Behnam Ben Taleblu of the Foundation for Defense of Democracies.
An administration led by Democratic nominee Joe Biden is likely to seek a reengagement with multilateral agreements and treaties involving Iran that U.S. President Trump's administration is believed to have unilaterally walked away from, says Behnam Ben Taleblu, senior fellow at the Foundation for Defense of Democracies.
The legality of the Trump administration triggering a "snapback" process on Iran sanctions in the United Nations Security Council is in a "murky space," given the U.S. left the 2015 nuclear deal that lifted these sanctions in the first place, says Stratfor's Emily Hawthorne.
Iran's show of force comes as a U.N.-imposed arms embargo is set to expire in October.
President Trump announces he's reimposing previously suspended UN sanctions on Iran. He says it's a snapback and not uncommon.
The Trump administration slapped fresh sanctions on two United Arab Emirates-based companies for providing material support to Iran's largest airline, the Treasury Department said Wednesday.
Many Gulf states see Israel as an "asset" because the country stands up to Iran, said Tzachi Hanegbi, an Israeli government minister.
China is probably glad to witness the ongoing U.S.-Iran tensions, partly because it drives a wedge between the U.S. and its European allies which weakens the U.S.' global power, says Jon Alterman of the Center for Strategic and International Studies.
Saudi Arabia, a key player when it comes to regional policy toward Israel, has remained eerily quiet on news of Israel's accord with the United Arab Emirates.
The U.S.-brokered peace deal between Israel and the United Arab Emirates is an irreversible "strategic shift" in the Middle East, says Anwar Gargash, the Emirati minister of state for foreign affairs.