WASHINGTON, D.C./BEIRUT: U.S. President Donald Trump says that the United States will target Pickaxe Mountain in Iran, warning that Washington would continue to strike the country hard.

Pickaxe Mountain, located near Iran's heavily damaged Natanz uranium enrichment facility, is a strongly protected site. It has two deep underground tunnel complexes that experts believe are beyond the reach of even the most powerful bunker-buster bombs in the U.S. arsenal.

Trump said on the Hugh Hewitt Show this week the United States would take out Pickaxe Mountain and told Iranians to be ready.

He said the site was being closely watched and that there was no activity there. He added that Iran was not doing well with its nuclear program, and that every time the U.S. heard about it, it destroyed it. He said Iran did not like talking about it, and added that the U.S. would likely target Pickaxe Mountain soon.

A day earlier, Trump said the United States was bringing back its blockade of Iranian shipping in the Gulf and would keep the Strait of Hormuz open for a fee after both sides exchanged more missile and drone attacks.

He said the U.S. would hit Iran very hard that night and again the next day, and added that there was nothing Iran could do about it.

At the same time, after restricting shipping through the Strait of Hormuz, Iran is now signaling it could take a more serious step by using its allies, the Houthis in Yemen, to shut the Bab el-Mandeb Strait, which leads to the Red Sea. This could open a new front against the United States and put two of the world's most important energy routes at risk.

As U.S. strikes inside Iran increase and Houthi attacks also rise, analysts say Iran is expanding the conflict and trying to put more pressure on Washington by threatening global trade and energy supplies beyond the Middle East.

Iran has already shown its power by disrupting traffic through the Strait of Hormuz. Now it appears ready to create a second pressure point at the Bab el-Mandeb Strait, a narrow waterway linking the Red Sea to the Gulf of Aden. A large amount of Saudi oil exports and global shipping pass through this route.

A senior Yemeni official warned that the country's armed forces were ready to close the Bab el-Mandeb Strait. He said this could push oil prices up to US$200 a barrel if Saudi Arabia continued its attacks on Yemen, according to a report on Iran's Press TV website.