Moscow on Thursday warned Washington against interfering in Iran's "internal affairs" after President Donald Trump pledged to help Iranians "take back" their government following protests.

The White House said it was weighing sanctions against those involved in a crackdown against the unrest, which has left 21 dead over five days.

"We warn the US against any attempt to interfere in the internal affairs of the Islamic Republic of Iran," deputy foreign minister Sergei Ryabkov said in an interview with state news agency TASS.

"Despite the many attempts to distort what is really going on (in Iran), I am sure that our neighbour, our friend, will overcome its current difficulties," Ryabkov said.

He also criticized a call by U.S. Ambassador to the United Nations Nikki Haley for an emergency UN Security Council meeting to discuss the violence.

Iran on Wednesday angrily accused the US at the UN of meddling in its domestic affairs.

Protests over economic problems broke out in Iran's second largest city Mashhad on Dec. 28 and quickly spread across the country, turning against the regime as a whole.

Tens of thousands of Iranians took to the streets in several cities on Wednesday for pro-regime rallies.