President Donald Trump said a conflict would Iran “wouldn’t last very long” because of American military might but also ruled out sending large numbers of ground troops into the region.

“I’m not talking boots on the ground, I’m not talking that we’re going to send a million soldiers,” he said during an interview with Fox Business on Wednesday morning. “I’m just saying if something would happen, it wouldn’t last very long.”

Additionally, Trump took aim at Japan and complained that the U.S. was responsible for protecting the island but getting nothing in return.

The commander-in-chief also traded insults with Iranian President Hassan Rouhani, who earlier questioned his mental fitness for the presidency. Trump said that “I don’t think (the Iranians) have smart leadership at all” and said the country “is going down the tubes.”

The comments come amid rising tensions between the countries following attacks on several oil tankers near the Strait of Hormuz that U.S. administration officials have blamed on Iran, and the downing of an American spy drone that Iranian officials claim was in their air space.

In the Fox Business interview, Trump repeated his previous statements that the United States had planned a significant military response to that attack, but “I didn’t want to kill 150 people when they shot down an unmanned drone … and a lot of people were very happy that I didn’t.”

Members of Congress have cautioned the White House against increasingly pointed rhetoric slipping into armed conflict. Several Democratic proposals circulating Capitol Hill would require congressional approval before any action against the country, but Republican lawmakers have broadly opposed the idea out of fear it could limit Trump’s ability to defend American interests.

Trump has said he hopes to avoid any such military conflict but also that his administration will ensure that Iranian researchers are not able to develop nuclear weapons. Last year, White House officials withdrew from a multi-nation deal with Iran to stop developing nuclear technology, saying that the agreement didn’t go far enough to limit Iranian aggression.

In recent days, Iranian leadership announced they would pull back parts of that deal, despite numerous European nation’s continued commitment to the terms.

Trump said he is confident that new economic sanctions are putting pressure on Iranian officials to re-evaluate their position.

“The sanctions are very biting,” he said. “When I took over Iran was a terror … They would have taken over the Middle East and they were going to make it very bad, very dead. Had I not been elected president they would have taken over Saudi Arabia, they would have taken over the entire Middle East.”

Trump also declared that “I’ve done great on the economy and I’ve done great with the military” during his term in office, but that his critics ignore those national security gains because of their political and personal opposition to him.

Trump, who is heading to Japan Wednesday for the Group of 20 (G-20) summit, also argued Japan wouldn’t pull its own weight in the event of a World War III.

“If Japan is attacked, we will fight World War III,” Trump said. “We will go in and we will protect them and we will fight with our lives and with our treasure. We will fight at all costs, right? But if we’re attacked, Japan doesn’t have to help us at all. They can watch it on a Sony television, the attack.”

The remarks come after Bloomberg reported Tuesday that Trump was contemplating withdrawing from the U.S.-Japan security alliance that requires the U.S. to defend Japan. Even so, Japanese chief government spokesman Yoshihide Suga said the U.S. confirmed withdrawing from the treaty is “incompatible with the U.S. government policy, per Reuters.