The U.S. imposed its “toughest ever” sanctions against Iran early Monday—and it has already sparked mass protests and a warning of war from President Hassan Rouhani. The sanctions—which mainly target oil and finance—came back into force Monday morning and are designed to reel in Iran’s missile and nuclear programs. The Trump administration reinstated all sanctions removed under the 2015 nuclear deal, which the U.S. withdrew itself from in May, and have reportedly added 300 more. Thousands of Iranians chanted “Death to America” at a rally Sunday and Rouhani has vowed to sell oil and break the sanctions. However, Foreign Minister Mohammad Javad Zarif, Iran’s top diplomat, told USA Today that Tehran would be open for talks if Trump changes his “approach” to discussing the agreement it abandoned earlier this year.