On Thursday, Sall promised to step down when his mandate ends on April 2, but said he could not yet set a new date for an election despite pressure to end a three-week electoral crisis that has fuelled unrest and fears of democratic backsliding.
He said political parties and civil society first needed to take part in talks scheduled for Monday, a day after the presidential vote was originally meant to be held.
Sixteen of the 19 presidential candidates rejected this proposal at a joint press conference in Dakar.
"By his actions, he is destroying the constitution and tailoring it to his needs," said a spokesperson for opposition candidate Khalifa Sall, calling on Sall to announce the election date as soon as possible.
"I categorically reject this sham of a dialogue," said fellow contender Anta Babacar in a statement. "You cannot hold a nation's future hostage."
Their decision deepens a political crisis that has gripped Senegal since early February when parliament approved a 10-month delay of the presidential election - a bill that was later ruled unconstitutional by a top court.
Civil society groups also refused to participate in talks. The Aar Sunu Election group said Sall was not following through on his promise to comply with the court ruling and called for the vote to be held before April 2.
Sall originally said the postponement was needed due to disputes he warned would undermine the credibility of the poll, but the move provoked widespread domestic and international backlash with some calling it an attempted "institutional coup."
(Reporting by Ngouda Dione, Cooper Inveen, Diadie Ba; Writing by Anait Miridzhanian; Editing by Alessandra Prentice and Ros Russell)
