* Plumes of black smoke billow across the capital
* Biggest display of public anger in over a year
* Similar protests broke out last year but fizzled out
* Internet access cut off
By Khalid Abdelaziz and Ulf Laessing
KHARTOUM, Sept 25 (Reuters) - Six Sudanese protesters were killed on Wednesday in clashes with security forces on a third day of unrest over a cut in fuel subsidies, medics and relatives said.
Protesters torched cars and petrol stations and threw rocks at police, who fired tear gas to try to disperse the biggest display of public anger against President Omar Hassan al-Bashir's government in more than a year.
Internet access was cut off across Sudan after activists began sharing images of the protests on social media. Shops remained closed for most of the day and long queues formed at petrol stations in Khartoum, one with 60 cars waiting. A major fire blocked one of the main traffic arteries in the capital.
Bashir has so far avoided the mass demonstrations that unseated rulers in Tunisia, Egypt and Yemen and led to civil wars in Libya and Syria. But simmering discontent over corruption and inflation appeared to boil over when prices of gasoline and cooking gas nearly doubled on Monday morning.
The deaths occurred in clashes in different parts of the capital, according to relatives and medical workers. Numerous plumes of black smoke rose into the skies above Khartoum.
"The people want the fall of the regime!" protesters chanted, echoing the trademark chant of the Arab Spring uprisings. "No, no to high prices!"
Mobs set fire to a university building and several petrol stations in Khartoum. They blocked a main road to the airport near the luxury Rotana hotel, used by diplomats and businessmen, and torched several cars in the parking lot, witnesses said.
A Reuters reporter saw police fire tear-gas grenades into a crowd while hundreds of officers and plainclothes security agents armed with guns or batons rushed to the city centre. Others were sitting on the roof of government buildings. Security agents drove away some 20 protesters in pickup trucks.
Many of Wednesday's protests around the capital mustered only a few dozen or at most a few hundred people and dispersed after a short time, making it hard to get an exact idea of how many had joined. But the total number in Khartoum was likely to have been in the thousands, and there were also demonstrations in the Red Sea coastal city of Port Sudan.
There was no immediate comment from the government on the unrest. Police officials could not be reached for comment.
Similar protests broke out in June last year after the government reduced fuel subsidies as part of a plan to contain its ballooning deficit, but they ended in the face of a security crackdown and Sudan's intense summer heat.
Bashir said on Sunday night that remaining subsidies would be lifted, but did not give details or a timeline. The next morning, fuel prices shot up.
The roots of Sudan's economic crisis lie in the secession of South Sudan in July 2011. The new nation took about three-quarters of Sudan's oil output, the lifeblood of its economy.
Crude exports were the government's main source of income and of the foreign currency it needs to import food and other goods for its 32 million people. Inflation soared and the pound lost over half its value against the dollar on the black market.
On Wednesday, the dollar bought about 8.2 Sudanese pounds on the black market, compared to about 7.3 pounds last week before the government announced it would trim fuel subsidies.
Khartoum had hoped to maintain some subsidies by boosting gold exports to replace oil revenues, but that plan was undermined by a recent fall in global gold prices.
The government says annual inflation eased to 23.8 percent in July from 37.1 percent in May, but independent analysts put the actual rate at 50 percent or even higher.
Two people were killed during protests in the Khartoum area on Tuesday, relatives who named the victims told Reuters. Police have confirmed only one death that day, saying a robber killed an unnamed man. Activists blamed government forces.
It remains to be seen whether the most recent round of protests will gather momentum or fizzle out like previous bouts of unrest in the last two years.
Bashir, who came to power in a coup in 1989, has weathered multiple armed insurgencies, years of crippling U.S. trade sanctions and a warrant for his arrest from the International Criminal Court.
Sudan's opposition parties, run by older men, are weak and divided, and have little appeal for young people demanding drastic improvements in living standards and political change.
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