Supreme Leader Ayatollah Ali Khamenei on Sunday urged Iran's armed forces to increase their power to "scare off" the enemy, according to his official website, as the country faces increased tension with the United States.

"Increase your power as much as you can, because your power scares off the enemy and forces it to retreat," the website quoted Khamenei as saying at a graduation ceremony for cadets of Iran's regular armed forces.

"Iran and the Iranian nation have resisted America and proven that, if a nation is not afraid of threats by bullies and relies on its own capabilities, it can force the superpowers to retreat and defeat them," Khamenei said during a visit to Iran's Caspian port city of Nowshahr.

State televison showed Khamenei watching drills by navy cadets and contacting the commander of naval forces Iran has sent to the Gulf of Aden, an area that suffered frequent piracy a few years ago, and off the coast of Yemen, where the Iran-alligned Houthi movement fights a Saudi-backed government.

"Your mission is valuable and your are able to completely secure the seas all around our dear country Iran with your wisdom and power," Khamenei told the commander through a videolink.

Saudi Arabia is leading a Sunni Arab coalition fighting the Houthis in the impoverished state on the tip of the Arabian peninsula.

Iran rejects accusations from Saudi Arabia that it is giving financial and military support to the Houthis in the struggle for Yemen, blaming the deepening crisis on Riyadh.