ALGIERS (Reuters) - Tens of thousands of Algerian protesters marched on Friday to demand that a presidential election next month be canceled until the old ruling guard step aside and the army quit politics.

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The marches, held in cities and towns across the country, marked the 41st consecutive weekly protest of a movement that has already forced the ruling hierarchy to jettison a veteran president and jail top officials.

The protest movement’s continued momentum now poses a major challenge to the military, which has pushed for the December 12 election as the only way to resolve the deadlock between the authorities and the nebulous, leaderless opposition movement.

Protesters on Friday chanted “No to the election”, “Free the detainees” and “the army should leave politics” as they marched through central Algiers. One protester held up a placard reading: “They have the vote. We have the veto”.

Since the election campaign officially began earlier this month, tensions have escalated, with more frequent demonstrations, more arrests, longer prison terms and scuffles between police and protesters in a provincial town on Wednesday.

Algeria’s main labor union, which is pro-government, plans a rare march on Saturday in Algiers to demonstrate in favor of the election.

The protests began in February as it became clear that veteran leader Abdelaziz Bouteflika planned to seek another presidential term in a vote originally scheduled for July.

As hundreds of thousands marched across the country, the army pushed him to quit in April. Dozens of senior figures, including a former intelligence chief, Bouteflika’s brother, government ministers and allied business tycoons were detained.

Several of them have been jailed for long terms on corruption charges and two former prime ministers, Ahmed Ouyahia and Abdelmalek Sellal, are to be prosecuted next week.

However, the protesters have demanded a more thorough purge of the ruling elite, which has controlled Algeria since winning independence from France in 1962, and the authorities have also arrested dozens of opposition figures and demonstrators.

Algeria, which relies heavily on oil and gas sales, has been hit hard by the crash in oil prices, halving its revenues from $60 billion to $30 billion.