Sall has faced growing calls to set a date for the presidential election after his abrupt delay of the February 25 poll triggered weeks of political crisis.
But in a televised interview late Thursday, he put off a decision on the date until after talks with political and social actors, due to begin Monday.
He said he hoped to reach an agreement by late Tuesday.
"We oppose all proposals for dialogue and demand that a date be set before April 2," one of the group of 16 candidates, Boubacar Camara told a press conference Friday.
Sall stressed during his TV appearance that his mandate would end as planned on April 2.
But he left open the question of when the vote would take place. When pressed, he added that he did not think it would be possible before April 2.
"We are calling for mobilization," said another presidential candidate Aliou Mamadou Dia.
He added that the group — which comprises 16 of the 19 candidates approved in January by the Constitutional Council —was working on an action plan to take place on Monday and Tuesday.
'Attempt at diversion'
A collective of some 40 Senegalese civil society groups also rejected Sall's proposed dialogue, describing it as "unacceptable" and an "attempt at diversion."
The Aar Sunu Election (Protect Our Election) collective also demanded the vote be held before April 2 in a statement published Friday.
The opposition has denounced Sall's last-minute move to delay the vote as a "constitutional coup," saying his party feared defeat at the ballot box.
The postponement plunged the traditionally stable West African country into turmoil and sparked unrest that has left four people dead.
Senegal's top constitutional body last week overturned the delay and called for the vote to be organised "as soon as possible."
Sall, who has been in power since 2012, said he delayed the election partly over concerns about a return to unrest seen in 2021 and last year.
He has since insisted he wants dialogue to calm tensions and promote peace and reconciliation.
'Sweeten the pill'
When asked about a poll date, Sall insisted that the forthcoming dialogue would decide "whether a consensus can be reached on the way forward."
If no agreement is reached, he said it would be up to the Constitutional Council to decide.
"Our position is (before) April 2, otherwise there will be a crisis," said Malick Diop, one of the organisers of Aar Sunu Election.
The collective mobilised several thousand people in the capital Dakar last weekend and is sticking to rallies planned for the coming days.
One candidate, Thierno Alassane Sall — no relation to the president — took to social media to accuse Sall of fresh manoeuvres to stay in office.
He said he suspected the president would select divided participants for the dialogue and then use a lack of consensus to stay until the transfer of power, beyond April 2.
"To sweeten the pill, Macky Sall is offering us an amnesty," he added.
During Thursday's interview, Sall said he was considering the possibility of provisional releases, pardons or an amnesty law for opposition figures including Ousmane Sonko and Bassirou Diomaye Faye.
DAKAR — Most candidates in Senegal's delayed presidential election and a large civil society collective said Friday they would refuse to take part in talks proposed by President Macky Sall to decide a date for the vote he postponed earlier this month.
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