Groups of policemen have appeared at major intersections in the Iranian capital Tehran, in apparent anticipation of unrest as the government makes sensitive cuts to subsidies.
President Mahmoud Ahmadinejad said cuts to energy and food subsidies are to come into force.
Under the new system, each car would receive 60 litres of fuel per month at a subsidised price of 25p per litre, a four-fold increase. Further petrol purchased would cost 45p a litre, compared with 25p before.
In 2007, angry protesters set dozens of petrol stations on fire after the system of fuel rationing was implemented.
Witnesses say clusters of riot police could be seen at every major square in the city. There has been no official explanation or report of disorder so far.