WASHINGTON — U.S. President Donald Trump said Monday that any country doing business with Iran will pay a 25 percent tariff on any business being done with the United States "effective immediately," as Washington is carefully watching Tehran's crackdown on anti-government protestors. Trump made the announcement in a social media post after White House press secretary Karoline Leavitt told Fox News that though diplomacy remains the president's "first option" regarding Iran, the use of military force would be among many options for the U.S. commander-in-chief. "Effective immediately, any Country doing business with the Islamic Republic of Iran will pay a Tariff of 25% on any and all business being done with the United States of America," he wrote on Truth Social. "This Order is final and conclusive," he added. Hundreds of protesters in the Islamic Republic are thought to have been killed in over two weeks of nationwide demonstrations by those dissatisfied with their country's economic difficulties and other issues, according to reports. Trump said earlier this month that if Iran "violentl