Vows by Algeria’s ailing president, Abdelaziz Bouteflika, to set early elections should he win a new term in April appear not to have satisfied the thousands of demonstrators who have rallied against his candidacy.

The youth who have been at the forefront of large-scale street protests against Mr. Bouteflika’s bid for a fifth term demonstrated overnight Sunday, while opposition figures denounced the president’s concessions as a sham.

Protesters said their principal grievance — that Mr. Bouteflika is maintaining his candidacy after 20 years in office despite having a stroke in 2013 that left him paralyzed and nearly mute — had not been satisfied. Mr. Bouteflika, 82, has not spoken publicly in seven years and appears only rarely in images, seemingly immobile with his eyes fixed in front of him.

They were not impressed by a letter read out on state television on Sunday by his campaign director, in which the Algerian president said he “would not be a candidate” in any future election.