Iran unveiled a new fighter jet as President Hassan Rouhani ratcheted up tension with the US by suggesting Washington would not attack the Islamic Republic because it was too powerful.

Iran has expanded its military presence in the region by sending troops to support President Bashar al-Assad in Syria's civil war, but years of sanctions have reduced its air force to several dozen old aircraft.

The new Kowsar, claimed to be a domestically-built jet, was unveiled at a ceremony as Mr Rouhani said Iran should be prepared to confront its enemies.

"We should make ourselves ready to fight against the military powers who want to take over our territory and resources," he said.

"Why does the United States not attack us? Because of our power, because it knows the consequences," he said.