The head of Iranian volunteer Basij forces says the United States is not in a position to threaten Iran, dismissing President Donald Trump's pugnacious Tweeter message addressed to President Hassan Rouhani as "psychological warfare."

"Trump's statements against Iran are psychological warfare. He is not in a position to act against Iran," Brigadier-General Gholam-Hossein Gheibparvar said on Monday.

Trump has threatened Iran with hardship "the likes of which few throughout history have ever suffered before" as the United States launched a campaign meant to foment unrest in the Islamic Republic.

Gheibparvar said the Iranian people and Armed Forces will stand up to the enemies, and will not back down, adding "our belief is that the way to felicity and progress is to resist and withstand ill-wishers and enemies."

"We will not step away from our revolutionary principles and beliefs, and will stand up to expansionists, arrogant powers, and bullies," he said.

"Those who fear this crazy president's psychological warfare will know that America will not be content with anything less than our annihilation," the commander added.

On Monday, Iran unveiled the mass-production line of a medium-range air-to-air missile, dubbed Fakour, in the presence of Defense Minister Brigadier General Amir Hatami.

Defense Minister Brigadier General Amir Hatami (C) inaugurates the mass-production line of Fakour air-to-air missile in Tehran, July 23, 2013. (Photo by Tasnim News Agency)

Hatami said the missile was being manufactured for the first time in Iran, adding the projectile had been designed and produced using state-of-the-art technology, and could be engaged against various aggressive aircraft within its operational range.

He also called the missile's mass production a key step towards enhancing the country's defensive power and effective deterrence capability.

The missile, Hatami said, had reached the mass-production stage despite US-led sanctions targeting Iran's missile industry.

"Today, we live in an environment, where we are surrounded by shameless enemies and mischievous people like the current rulers of the US, and some of its allies, who do not understand anything other than the language of force," the defense chief noted.

In line with the instructions of Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei, Iran would give a proportionate response to any threat, Hatami added.