Iran's supreme leader on Sunday threw his support behind a decision to hike petrol prices, a move that sparked nationwide unrest in which he said "some lost their lives".

Ayatollah Ali Khamenei blamed "hooligans" for damaging property and said "all the centres of the world's wickedness against us have cheered" the street protests.

Several people were wounded and dozens arrested in two days of demonstrations that saw motorists block highways and others attack public property in cities across the Islamic republic.

In a speech aired on state television, Khamenei said "some lost their lives and some centres were damaged" in the unrest.

The protests flared hours after it was announced in the early hours of Friday that the price of petrol would be raised by 50 percent for the first 60 litres (16 gallons) and by 300 percent for anything above that each month.

The scheme was agreed by the High Council of Economic Coordination made up of the president, parliament speaker and judiciary chief.

Khamenei said that "I am not an expert and there are different opinions but I had said that if the heads of the three branches make a decision I will support it.

"The heads of the branches made a decision with the backing of expert opinion and naturally it must be implemented," he said.

"Some people would definitely get upset over this decision... but damaging and setting fire (to property) is not something (normal) people would do. It is hooligans."

Following his speech, parliament cancelled a motion to reverse the petrol price hike, semi-official news agency ISNA reported.