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North African neighbours Algeria and Tunisia have both been convulsed by widespread rioting and fatal clashes with police in the past few days.

The timing of the riots raises the question of whether they are part of the same trend.

If they are, that could send a chill wind through governments elsewhere in the Arab world, where people have many of the same grievances.

George Joffe, a specialist in North African affairs at Cambridge University, sees certain shared characteristics, but no common cause.

"Both countries' governments are extremely insensitive to popular sentiment, both countries have seen a dramatic rise in food prices," he said.

"But [the riots] are not related, in that they started for very different reasons. I don't see a link."

"It's simply the case that in both countries, people lead miserable lives," he added.

The main thing the two cases have in common is demography.

In both Algeria and Tunisia, high birth-rates have led to an explosion in the number of young people of job-seeking age.

At the same time, the economies of both countries - while outpacing growth in developing economies in the past few years - have not grown fast enough to meet the demand for jobs.

Algeria and Tunisia also shared the method people used to express their unhappiness: young people taking to the streets, throwing petrol bombs and stones at police, and ransacking buildings.

This may be because in both countries there is only limited political discourse and no vibrant opposition through which people can channel their grievances.

But here the two sets of protests diverge.

In Algeria, it was a limited flare-up of built-up frustration about tough living conditions with no far-reaching political implications.

In Tunisia, the unrest is turning into a challenge to the rule of President Zine al-Abidine Ben Ali.

"It's the first time there's been a major disturbance of this kind in Tunisia, and it's a warning to the president of the danger of creating a totally unnecessary dictatorship," said Mr Joffe.

"He needs to think very carefully about how he proceeds with his policies from here," he added.

In Tunisia, the protests' initial focus was youth unemployment and police heavy-handedness, but animosity towards Ben Ali, who has run the country since 1987, has turned into a constant theme.

A video circulating on social media websites used by opponents of the Tunisian government on Monday showed a group of men trying to set fire to a poster of Ben Ali - similar to the ones which hang in every shop and public building in Tunisia.

Discussion threads about Tunisia on Twitter, another social networking tool, are full of rhetoric aimed at the president.

"Ben Ali, do you see the wave that will sweep you away?" said one post. "Ben Ali must be held accountable," said another.

A third post said: "Let us turn the protests/uprising in Tunisia into the first socio-political revolution powered by social networks."

Next door in Algeria, very few of the rioters articulated any political demands; they were just angry about sharp rises in the price of sugar and cooking oil.

The government, with deep pockets from the export of oil and gas, quickly said it would curb price rises, and since then the rioting has tapered off.

Algeria has already had its "people power revolution" - the year after Ben Ali took office.

Then, days of intense rioting in the capital led the authorities to loosen controls on society and the economy, allowing private newspapers and multi-party elections for the first time.

That flowering of freedom quickly degenerated into a conflict between security forces and Islamist rebels which killed 200,000 people, according to some estimates, from which Algeria is still emerging.

After that experience, few Algerians have any appetite for any more political transformations.

By contrast, Tunisia has been a model of stability and has only had two heads of state since independence from France.

Some of the young Tunisians clashing with police over the past few days feel it is their turn to try a revolution.