Riots have swept across the Ugandan capital, Kampala, in the biggest anti-government protest in sub-Saharan Africa so far this year.

A Ugandan protestor shouts near a burning barricade in Kampala after Ugandan opposition leader Kizze Besigye was arrested for the fourth time this month. (Photograph: Marc Hofer/AFP/Getty Images) Security forces have launched a brutal crackdown, opening fire on unarmed civilians with live rounds, rubber bullets and teargas. Two people have been killed, more than 120 wounded and around 360 arrested. Women and girls have been among those beaten, according to witnesses.

Two weeks of growing unrest – sparked by rising food and fuel prices – have gained fresh impetus after the violent arrest of the opposition leader Kizza Besigye on Thursday. Critics say President Yoweri Museveni, in power for 25 years, is losing his grip. They claim his wildly disproportionate crackdown on Besigye's "walk to work" protests smacks of panic and is sowing the seeds of popular revolt.

"I thought the police were going to kill me," said Andrew Kibwka, 18, after police with heavy sticks rained blows on him. "I was telling them I'm harmless but they just carried on. I did nothing to provoke them. They beat me because I was running away."

Some point to the political earthquakes in Tunisia, Egypt and Libya, and wonder if the aftershocks could reach tyrannies south of the Sahara. Already there are pockets of unrest from Burkina Faso to Senegal to Swaziland. Even South Africa, reputed anchor of the continent, is tormented by deadly protests over poor public service delivery.

In Uganda there is an inchoate revolution struggling to be born. Protests have spread to several towns, leaving seven people dead and hundreds in jail. The riots, in which roads have been barricaded with burning tyres and vehicles pelted with rocks, mark a new level of defiance. Facebook and Twitter, which the government unsuccessfully tried to block, are reverberating with dissent. Museveni's heavyhanded attempts to put out the fire only appear to be fanning its flames.

The subversion here began on 11 April with nothing so spectacular as an act of self-immolation: rather, a defeated politician and half a dozen allies walking down a street. The walk to work campaign is intended to highlight the soaring prices of fuel and food, which leave many Ugandans unable to afford public transport.

If Besigye, who has lost three elections to Museveni, had been ignored the piece of theatre might have fizzled out. Instead riot police blocked the group, unleashed teargas and arrested Besigye. At a stroke this waning establishment figure was reborn as a hero of resistance.

Ssemujju Ibrahim Nganda, an MP-elect for Besigye's Forum for Democratic Change, recalled the innocuous beginnings of walk to work. "We never intended to have a Tahrir Square to remove Museveni," he said. "We just wanted a reawakening of the people. We started walking, the simplest thing on Earth, and Museveni said you can't."

At the third protest Besigye was hit in the hand by a rubber bullet. Images of him with hand bandaged and in a sling gave the opposition a publicity coup. With each walk he has attracted more followers like a pied piper.

Nganda, who was jailed for five days for taking part in a walk, said: "When you start a campaign you never know what the response will be. I didn't know we'd have any people following; nobody knew. Museveni's brutal reaction is what raised its profile beyond our expectations. It's dominating the media, the opposition, even Museveni himself."

The 37-year-old said Ugandans would prove as determined as their north African counterparts. "I don't think when the Tunisians started they knew it would be the end of Ben Ali, or when the Egyptians started they knew they would get rid of Mubarak. Nobody can be sure what shape it will take in Uganda but we are going to continue until Museveni leaves."

Besigye, 54, who was Museveni's personal doctor during the bush war against former president Milton Obote, was detained again in Kampala on Thursday after police smashed their way into his vehicle and shot pepper spray into his eyes, potentially causing permanent damage to his sight.

Just an hour earlier he had admitted he was hesitant to draw close comparisons with Egypt and Tunisia. "The only parallel goes to the extent that people are discontented with what is going on and their governments are non-responsive," he said. "There is a loss of trust between the regime and the people. I think that is the only parallel I can see. How this popular discontent is channelled is always governed by the unique qualities of governments."

Asked if he was prepared to die for the cause, Besigye replied: "I am not setting out to become a martyr of anything. I am simply asserting my citizen's rights, which are inherent, which are not offered by the state and which I am determined to defend at all costs."

Commodity prices could be the spark in a Ugandan tinderbox of resentment over corruption and neglected public services. Museveni has refused to copy neighbouring Kenya by cutting taxes on fuel. And with unfortunate timing his recent re-election campaign is estimated to have cost $350m (£210m) with a further $1.3m (£781,000) allotted to his inauguration ceremony, while a bill for new military fighter jets stands at $740m (£445m).

Public anger was burning on a street where no car was safe from flying stones. Robert Mayanja, a self-described activist, said: "What they are doing now shows that Museveni rigged the last election. If you look at Uganda, why should we vote for him after 25 years? We have high prices, we have hospitals without medicine."

Mayanja, 31, said a repeat of the revolts in Egypt and Tunisia was "definitely" possible. "What we are seeing here are people who are not armed but are taking a stand against armed forces," he said. "People are ready. It's just a question of time.

"We know they are going to arrest many people and put them in torture chambers. We know this regime has expired. These are the signs."

In Ntinda district angry youths shouted and hurled stones and chunks of concrete at passing cars. On one corner a man ran up to a council vehicle as it drove by and smashed the driver's window with a rock, raising cheers from onlookers.

A teacher, who gave his name only as Nixon, 32, said he could not imagine an Egypt-like revolt in the short term. "But in the long term I believe it can happen," he said. "The military is still strong and many of the soldiers are unwilling to turn to the side of the people. But in time they might get tired of beating the people.

"I really look forward to it. As your friends are beaten and arrested, the professionals need to come out and organise the people."

A young population often seen as politically apathetic has reached unexpected levels of activism. People who used to bolt at the first whiff of teargas are losing their fear. But there are serious doubts over whether a critical mass of Ugandans have the will or the means to drive the president out. He retains a vice-like hold on the military and police.

Rosebell Kagumire, a journalist blogging and tweeting the political crisis, said: "Most people on Twitter are anti-Museveni but there is not a firm opinion on what to do now. They don't expect him to go anywhere soon. He owns the army and his government won't stop at anything.

"It's hard to get people to believe going to the streets will change anything, especially when they know the government is prepared to kill half of them. Ugandans have not reached that level yet."

Museveni, whose recent election victory has been denounced as fraudulent, is confident he can avoid the fate of Arab leaders. "Nobody can take over power through an uprising," he said recently. "Whoever thinks like that, I pity such a person."

His spokesman, Tamale Mirundi, added: "In Tunisia and Egypt democracy was lacking; in Uganda we elect our leaders at every level. The president organised and campaigned in transparent elections. Besigye cannot say he was cheated and that is why he is jumping on oil prices."

Mirundi played down the power of the internet. "Go to the villages. How many people can access Facebook? Very few. Who knows Facebook? Very few. Facebook cannot create a politician in our country. Facebook cannot create a problem."

Yet every day in Uganda, and elsewhere in Africa, new people are connecting and interacting for the first time. "Uganda is sitting on a time bomb," tweeted Richo Nuwagaba . "It's just a matter of time. I am scared."