Iranian President Hassan Rouhani vowed to defy US sanctions as penalties targeting the country's oil-and-gas sector. The most biting round of sanctions since US President Donald Trump pulled out of the landmark 2015 deal to curtail Iran's nuclear program came into force Monday. The move targets Iran's oil-and-gas, shipbuilding, shipping and banking industries. Iran will "proudly break the unjust sanctions," Rouhani said in public remarks during a cabinet meeting Monday. "We must make the Americans understand in clear language that they cannot deal with us with force, pressure and sanctions."