Turbulence rocked the oil market after President Trump announced the United States will exit the Iran nuclear deal and impose "powerful" sanctions on the country.

In a roller-coaster day of trading, US crude oil prices fell more than 4% before the announcement, rebounded as Trump spoke, dropped again and then recovered later in the day to trade above $70 once more.

Trump slammed the Iran nuclear deal as a "horrible, one-sided deal" that was "defective at its core."

After he spoke, Trump signed a memorandum that he said would begin reinstating American sanctions on the Iranian regime.

Related: Trump withdraws US from Iran nuclear deal

Those sanctions could take months to go into effect as the US government develops guidance for companies and banks.

The Treasury Department announced that the sanctions will "come back into full effect" following adjustment periods, including six months for sanctions targeting Iran's oil trade and energy industry.

The key for the energy market is how much Trump's tough stance on Iran will restrict the flow of crude out of the OPEC nation. Analysts say that up to 1 million barrels per day of Iranian crude is at stake.

That could hold prices down in a market that has already been short on supply because of production cuts by OPEC and Russia. Crude oil prices settled above $70 a barrel on Monday for the first time since late 2014.

The ultimate impact will be determined by how Iran's major customers — China, the European Union, India and South Korea — respond to Trump's sanctions.

"Any nation that helps Iran in its quest for nuclear weapons could also be strongly sanctioned by the United States," Trump said.

— CNN's Kevin Liptak and CNNMoney's Donna Borak contributed to this report.