President Trump announced Monday that he will impose additional economic sanctions on Iran in response to recent acts of aggression that have sharply escalated tensions between the two nations in recent weeks.“We will continue to increase pressure on Tehran,” Trump said in the Oval Office before signing an executive order imposing the new sanctions. “Never can Iran have a nuclear weapon.”The executive order, which expands upon existing sanctions that have effectively deprived Iran of oil-export revenue, freezes the assets of officials serving at the highest levels of the Iranian government, including those assets held by the country's supreme leader, Ayatollah Khomeini.Addressing reporters from the White House briefing room after the executive order was signed, Secretary of the Treasury Steven Mnuchin dismissed the suggestion that the latest round of sanctions was “symbolic,” pointing out that order will effectively “lock up tens of billions of dollars” previously held by the most influential people in Iranian government.The latest round of sanctions come after the Pentagon announced Thursday that an Iranian surface-to-air missile had downed a U.S. military-surveillance drone flying above the Strait of Hormuz, a major waterway through which one-third of the world's oil supply flows.In response, Trump ordered a missile strike against a number of Iranian radar facilities, but reversed himself Thursday evening minutes before the strike was to be carried out after concluding that the resulting 150 casualties would represent a “disproportionate response” to the downing of an unmanned drone.During the Monday Oval Office signing ceremony, Trump touted the “restraint” displayed by his administration but warned that he may not show such restraint going forward if Iran continues to behave aggressively.The drone conflagration further increased tensions that were heightened significantly the week prior, when Secretary of State Mike Pompeo announced that Iran was responsible for explosive attacks on two foreign oil tankers passing through the Strait of Hormuz, the fifth and sixth such attacks in the region since May.Iran has denied responsibility for the attacks, but U.S. intelligence officials maintain that the Islamic republic is the only actor in the region with the motivation and capability to plant sophisticated explosives on the tankers.