Demonstrations were held in the capital Jakarta and other cities as lawmakers gathered to decide on budget amendments that will pave the way for the government to announce the first price hike since 2008.
Fuel prices have long been a flashpoint issue in Indonesia, with economists arguing that huge government subsidies are damaging Southeast Asia's top economy.
Millions are opposed to lowering the payouts, which keep down the cost of living.
"The situation became somewhat chaotic and the police had to fire tear gas to disperse them," said the spokesman, who like many Indonesians goes by one name.
Nobody managed to enter and the situation was under control, he added.
A male journalist was hit near the eye by a tear gas shell casing and was receiving hospital treatment, the spokesman said.
In Jakarta, some 3,000 demonstrators gathered outside the national parliament in light rain, setting fire to tyres and waving banners that read "Reject the fuel price rise" and "hang SBY" (President Susilo Bambang Yudhoyono).
About 19,000 police and military personnel were deployed across Jakarta, police said.
In the city of Makassar, on Sulawesi island, around 500 university students and teachers protested, burning tyres and yelling "revolution".
While only a small percentage of Indonesians are private car owners, the plan to increase the price of petrol by 44 per cent is expected to push up the cost of everyday goods as they will be more expensive to transport.
The state budget amendments will provide financial assistance to poor households, paving the way for Yudhoyono to announce an increase.