A report from the Iranian capital says there is heightened security in Tehran's streets as the Iranian government's cuts to economic subsidies come into force.
AP quoted witnesses as saying clusters of riot police could be seen at every major square in the city.
There has been no official explanation, but their presence follows an announcement from President Mahmud Ahmadinejad that cuts of energy and food subsidies will start from today.
In 2007, angry protesters set dozens of gas stations on fire after fuel rationing was implemented.
Under the new system, each car will receive 60 liters of fuel per month at a subsidized price of 40 cents per liter, a fourfold price increase.
Further gasoline purchased will cost 70 cents a liter, compared to 40 cents before.
compiled from agency reports