United States President Donald Trump on Saturday said that the country will impose “major additional sanctions” on Iran from Monday, in a bid to prevent the country from obtaining nuclear weapons. Trump’s threat came even as Tehran warned Washington that that it will pay a heavy price if it fires one bullet.

The tension between both the countries renewed last week after Iran shot down an American spy drone over the Strait of Hormuz. While Tehran claimed the drone violated its airspace, the US maintained it was shot down over international waters.

“We are putting major additional Sanctions on Iran on Monday,” Trump, who has also deployed additional troops to the Middle East, said in a tweet. “I look forward to the day that Sanctions come off Iran, And they become a productive and prosperous nation again – The sooner the better!”

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Trump also claimed that military action against Iran was still an option. This came days after he said he had ordered a military strike on Iran but pulled back at the last minute as 150 people would die. “I never called the strike against Iran ‘BACK,’ as people are incorrectly reporting,” Trump said in another tweet. “I just stopped it from going forward at this time!”

The incident came at a time when the United States accused Iran of attacking two of its oil tankers in the Gulf of Oman on June 13. Hormozgan borders the Strait of Hormuz, where the tankers were located. The US military has also accused Iran of firing a missile at a drone that had responded to the explosions. In May, Washington had alleged Tehran had orchestrated a similar attack in which four tankers in the same area were damaged.