Iran's Supreme Leader, Ayatollah Ali Khamenei, has accused "enemies" of Iran of stirring up unrest to try to overthrow the Islamic Republic.
He said those who opposed Tehran hoped to use protests to strike a blow at the country.
A deadly building collapse in the south last month sparked further protests blaming authorities for the incident.
The ayatollah has long insisted that US sanctions are to blame for the soaring prices of basic foods in the country.
"Today the enemy counts on popular demonstrations to strike the Islamic system," he said in a televised address on Saturday.
The enemy "hopes to turn the people against the Islamic Republic by psychological means, through the internet, money, and the mobilisation of mercenaries," he said.
"The Americans and the Westerners made miscalculations in the past on various questions," he added. "Still today, it's a miscalculation that they think they can make the Iranian nation oppose the Islamic Republic."
The disaster has been blamed on structural faults, poor safety standards and the flouting of regulations.
Thirteen people have been arrested, including the city's mayor.
However, protesters are blaming the wider authorities, accusing them of negligence and corruption.