A Revolutionary Guards commander said Iran would use its missiles if its security is under threat, as the elite force defied new U.S. sanctions on its missile programme by holding a military exercise on Saturday, February 4, according to Reuters.

Tensions between Tehran and Washington have risen since a recent Iranian ballistic missile test which prompted U.S. President Donald Trump's administration to impose sanctions on individuals and entities linked to the Revolutionary Guards.

Trump's national security adviser Michael Flynn said the Washington was putting Iran on notice over its "destabilising activity", and Trump tweeted Tehran was "playing with fire"

"We are working day and night to protect Iran’s security," head of Revolutionary Guards' aerospace unit, Brigadier General Amir Ali Hajizadeh was quoted as saying by Tasnim news agency.

"If we see smallest misstep from the enemies, our roaring missiles will fall on their heads," he added.

Despite the heated words, U.S. Defense Secretary Jim Mattis said on Saturday he was not considering raising the number of U.S. forces in the Middle East to address Iran's "misbehavior", but warned that the world would not ignore Iranian activities.

Iran's Revolutionary Guards is holding the military exercise in Semnan province on Saturday to test missile and radar systems and to "showcase the power of Iran's revolution and to dismiss the sanctions," according to the force's website.

Dismissing Trump's comments that "nothing is off the table" in dealing with Tehran, the commander of Iran's ground forces said on Saturday that the Islamic Republic has been hearing such threats since its 1979 revolution.

"The defence capability and the offensive prowess of Iran's armed forces would make America or any other enemy regretful of any incursion," Ahmad Reza Pourdastan was quoted as saying by ISNA.