Algiers (AFP) - Algerian demonstrators kept up protests Wednesday against the ruling elite despite a pledge from the interim head of state to hold "transparent" presidential elections following veteran leader Abdelaziz Bouteflika's resignation.

The army weighed in with assurances of its own, vowing to guarantee "transparency and integrity" during the transition. But it also warned against attempts to "destabilise" the country.

Chants of "Go away Bensalah!" and "A free Algeria!" rang out from early morning from thousands of demonstrators gathered under police surveillance in the capital's May 1 Square and near the Grand Post Office, epicentres of anti-regime rallies over the past seven weeks. 

Lawmakers on Tuesday selected upper house speaker Abdelkader Bensalah as Algeria's first new president in 20 years in line with constitutional rules, but the appointment failed to meet the demands of demonstrators pushing for the whole of Bouteflika's entourage to stand down.

Bensalah, 77, a close ally of Bouteflika and key figure of his regime, pledged to organise a "transparent" presidential election within 90 days as laid out by the constitution, which bars him from running.

But students and magistrates on Wednesday called for demonstrators to keep up their rallies and marches in Tunis and cities across the North African country.

Army chief General Ahmed Gaid Salah, quoted in a defence ministry statement, said the military would ensure the transition follows the "rules of transparency and integrity, and the laws of the republic".

But he warned against "slogans aimed at leading the country to a constitutional void and destroying state institutions".

"With the start of the new phase and continued marches, we deplore the emergence of attempts by certain foreign parties... to destabilise the country", he said, without pointing fingers.

The army chief also signalled that the military would safeguard Algeria's institutions.

"It is unreasonable to manage the transition period without the institutions," Salah said, warning that such a scenario "could compromise all that has been achieved to this day since independence" from France in 1962.

For the first time in the wave of demonstrations which have swept Algiers since mid-February, police fired tear gas and water cannons Tuesday to try to disperse a protest by students.

"What happened yesterday was a violation of our right to demonstrate," said 22-year-old journalism student Asma. "We'll carry on every day if needed until the last of the (ruling) clan is out."

All eyes on Friday turnout

Since Bouteflika announced his resignation on April 2 after losing the military's support, the demonstrators have urged that regime insiders be excluded from the political transition.

All eyes are now focused on the turnout on the streets on Friday, the traditional day of protests in Algeria, and whether the authorities will adopt a tougher line and step up security measures.

For Mohamed Hennad, a political sciences professor at the University of Algiers, "the balance of forces will favour the street if it's a large mobilisation on Friday" as in past weeks.

But the appointment of Bensalah despite the protesters' opposition could signal "a change in the position of the authorities towards the demonstrators", according to Oran newspaper.

"There is like a return to the political stick against those who from now on oppose the natural course of events," it warned in an editorial.

For many ordinary Algerians, the interim president's assurance of a constitutional transition to a post-Bouteflika future has fallen short of easing their concerns.

"Bensalah is a leftover of the system... For the past twenty years, they've made us promises. The result: they've taken everything and left the people in poverty," said Lahcen, 26, who works in an Algiers cafe for a monthly salary of 25,000 dinars (about $200).

"What we want is a free election that is really democratic," he said.

The protest movement is calling for a new transitional framework that is committed to deep reforms.

The ailing Bouteflika finally stepped down at the age of 82 after weeks of demonstrations triggered by his bid for a fifth term in office.

After two decades in power, he had lost the backing of key supporters including the armed forces chief.