TEHRAN: Protests in Iran continued despite the president saying that the unrest "is nothing".

Anti-government chanting and burning cars were reported on the fifth day of unrest, while police said an officer was killed in a central city and others wounded.

At least 20 people are believed to have died in the clashes so far.

President Hassan Rouhani said protests were an "opportunity, not a threat" but vowed to crack down on "lawbreakers". The US meanwhile stepped up support for the protesters' "bold resistance".

The protests began last Thursday in the city of Mashhad, initially against price rises and corruption but now with wider anti-government sentiment.

The Mehr news agency reported a taxi being set alight. Police had used tear gas and water cannon the previous evening to quell a rally in Tehran's Engheleb Square.

State media were also quoting a police spokesman as saying that shots had been fired at police in Najafabad, near Isfahan in central Iran, killing one officer and wounding three.

Reuters news agency reported that a police station in the town of Qahderijan was partly set on fire amid clashes between security forces and protesters trying to occupy the building. Unconfirmed reports suggested several casualties, it added.

Social media postings spoke of fresh protests in Birjand in the east, Kermanshah in the west and Shadegan in the far south-west.