President Donald Trump signed an executive order Monday imposing additional sanctions on Iran following the country's shoot-down last week of a U.S. military surveillance drone.

The United States already has sanctions on the country that were reimposed after pulling out of a 2015 nuclear accord that the U.S. and other nations reached with Iran in an effort to put an end to its nuclear weapons aspirations.

The new sanctions will cut off Iranian Supreme Leader Ayatollah Ali Khamenei, his office and others from financial instruments, according to CNN. 

“We’ve done very massive sanctions. We’re increasing the sanctions now,” the president told NBC over the weekend.

What Happened

Brian Hook, the U.S. special representative to Iran, said on CNBC over the weekend that the goal of tightening the screws on Tehran now is to resume negotiations.

“Ultimately we would like to have a new deal that addresses Iran’s regional aggression, the missile program, and its nuclear program,” Hook said. “In order to do that, it is going to take pressure. And in order to get Iran to change its behavior, it is going to take a lot of pressure. So we are going to increase our sanctions on Iran.”

In addition to the attack last week on the drone, Washington blames Iran for two recent attacks on oil tankers in the Persian Gulf. American officials said the unmanned aircraft was over international waters in the Strait of Hormuz, while Iran said it was over Iranian territory.

Trump approved an airstrike in retaliation, but then backed off.

Iran cannot have Nuclear Weapons! Under the terrible Obama plan, they would have been on their way to Nuclear in a short number of years, and existing verification is not acceptable. We are putting major additional Sanctions on Iran on Monday. I look forward to the day that.....

— Donald J. Trump (@realDonaldTrump) June 22, 2019

Why It's Important

The new sanctions will "lock up literally billions of dollars in assets," said Treasury Secretary Steven Mnuchin, according to CNN. 

Several European nations, as well as China and Russia, oppose the U.S. increasing sanctions on Iran.

Oil prices were down on Monday, as was the United States Oil Fund LP USO, which was trading down more than 1% at $11.84 at the time of publication. 

The Standard & Poor's 500 ETF Trust was up slightly at $294.16.