U.S. President Donald Trump says he will impose more sanctions against Iran in an effort to prevent Tehran from obtaining nuclear weapons, adding that military action was still a possibility.

Trump, who was speaking to reporters at the White House on June 21, made his comments a day after revealing he called off military action against Iran in retaliation for the downing of a U.S. military drone.

Tehran has warned the United States of serious consequences for the entire Middle East if Washington moves aggressively against Iran amid escalating tensions between the two countries.

"We are putting additional sanctions on Iran," Trump said. "In some cases, we are going slowly, but in other cases we are moving rapidly."

Trump added: "We're not going to have Iran have a nuclear weapon. When they agree to that, they're going to have a wealthy country. They're going to be so happy, and I'm going to be their best friend. I hope that happens."

Trump spoke to reporters as he prepared to leave for the presidential retreat Camp David, where he said he would be deliberating on Iran.

Tensions between Tehran and Washington have spiked since an Iranian missile destroyed a U.S. Global Hawk surveillance drone on June 20.

Iran has said the drone was shot down over its territory while Washington said it occurred in international airspace over the Strait of Hormuz.

Based on reporting by Reuters and AFP