Iran's President Hassan Rouhani on Friday dismissed new US sanctions as unable to break the Islamic republic's "resistance" and said Washington has already done all it can to pressure Tehran.

US President Donald Trump's administration imposed sweeping sanctions on Iran's banking sector on Thursday by designating 18 major Iranian banks to "stop illicit access to US dollars".

"The Americans have so far done all they could against the great nation of Iran," Rouhani said, according to his official website.

"They cannot break the resistance of the Iranian nation with these inhumane" actions, he added.

According to Rouhani, the US administration is following "domestic aims" by such "political-propaganda attempts".

The sanctions are part of Washington's policy of "maximum pressure" against Tehran aimed at reining in the Islamic republic, the arch-foe of US allies Saudi Arabia and Israel. 

They were reimposed after Trump in 2018 unilaterally withdrew the US from a landmark accord with world powers and Iran, which limited the Islamic republic's nuclear programme in exchange for international sanctions relief.

The US Treasury Department said it was exempting transactions in humanitarian goods such as food and medicine.

But Rouhani said the sanctions are "attempts to create serious obstacles in fund transfers for medicine and food" and called them "cruel, terrorist and inhumane".

He also called on the world's "human rights advocates" to condemn the move.

The step could largely cut off the nation of 80 million people from the world's financial system just as it tries to cope with the Covid-19 pandemic.