In his Tuesday morning tweet... U.S. President Donald Trump warned that countries trading with Iran.... will not be doing business with Washington... as new sanctions on Tehran took effect overnight. <br />Ro Aram reports. <br /> President Trump's warning seems to be aimed at the European Union.<br />That is because the EU is trying to protect European businesses that are trading in Iran from facing U.S. sanctions. <br />In his tweet, President Trump said the latest sanctions on Iran were the most biting sanctions ever imposed, adding they will "ratchet up to yet another level" in November.<br />Washington is rolling out unilateral sanctions on Iran in stages following Trump's decision to withdraw the U.S. from the 2015 Iran nuclear deal.<br />The next round of punitive measures will come into effect in November and will target Iran's oil industry.<br /> The EU's foreign policy chief, Federica Mogherini, responded to President Trump's tweet by urging European firms to ignore the White House. <br />Also on Tuesday a blocking statute aimed at protecting EU firms took effect.<br />It involves possible punishments to European companies if they comply with Washington's demands, while offering them a chance to sue the U.S. for interference.<br />Russia, which remains a signatory of the 2015 deal along with the EU and others, also slammed the U.S. sanctions on Iran. <br /> Moscow's foreign ministry issued a statement saying Russia will do everything necessary to save the deal and protect its economic relationship with Tehran. <br />Ro Aram, Arirang News. <br />