US sanctions against Iran refer to economic, commercial, scientific and military sanctions imposed by the United States Office of Foreign Assets Control under US pressure through the UN Security Council. The sanctions now include a ban on dealing with Iran by the United States, a ban on the sale of aircraft and repair of spare parts to Iranian airlines, the various economic, financial and industrial sectors, mainly the oil sector, which is the main source of income for the hard currency that Iran needs.
The Trump Administration has imposed new sanctions on Iran’s oil exports, on November 5th. What is markedly different about this round of sanctions is that this time, the United States is doing it alone.
The Iranian economy has been weak in recent months as companies have distanced themselves from Iran to avoid US sanctions. Iran's biggest economic challenge is the drop in demand for its oil. Oil sales are the largest source of hard currency in Iran and are responsible for an important component of its budget. Oil exports reached about 2.3 million barrels per day during September 2017, but fell to 1.7 million barrels a day from September 2018. 
Iran's economic growth is expected to decrease by 1.5% in 2018 and another 3.6% in 2019.
However, Iran has taken a number of measures to mitigate the impact of U.S. sanctions. Beginning in the spring, the Central Bank of Iran sped up plans to unify the official and unofficial exchange rates to limit the impact of U.S. sanctions on the Iranian rial, although that plan was largely unsuccessful at halting the currency’s depreciation.
"We urge countries to reduce or end their imports of Iranian oil," Trump said. "Perhaps the Iranian regime is changing its dangerous and destabilizing behavior and reintegrating into the global economy."