Senegal plunged further into the unknown on Friday after the top constitutional body overturned President Macky Sall's contentious decision to postpone this month's presidential election.

It is yet to be seen how and when the vote will now take place, with Sall so far offering no comment on the historic ruling by the Constitutional Council.

His staff told the media they had "taken note" of the decision, without questioning the verdict, which cannot be appealed.

Sall's last-minute move to postpone the February 25 poll triggered Senegal's worst crisis in decades, sparking widespread outcry and prompting deadly protests in what is often seen as a bastion of stability in coup-hit West Africa.

Parliament later approved the delay until December 15, but only after security forces entered the building and removed some opposition lawmakers who opposed the bill.

The vote paved the way for Sall -- whose second term is due to expire in April -- to remain in office until a successor was installed, probably not before 2025.

Three people have been killed during demonstrations against the delay, with security forces repressing attempts to mobilise.

Opposition and civil society groups called for fresh protests on Friday and Saturday.

The Constitutional Council's decision late Thursday to overturn the vote delay was praised by opposition figures.

They had decried Sall's move as a "constitutional coup", saying his party feared defeat at the ballot box for its candidate Prime Minister Amadou Ba.

The Constitutional Council said it was "impossible to organise the presidential election on the initially scheduled date" but invited "the competent authorities to hold it as soon as possible".

The constitutional body also reiterated the fixed nature of the five-year presidential term.

Sall's term in office officially expires on April 2 and the head of state has repeatedly said he will not stand for a third term.

- 'Historic' -

The Constitutional Council in January approved 20 candidates to run in the presidential election.

It now remains to be seen whether the same list of candidates will be put forward again, and when the vote would take place -- it is widely understood it cannot be held on February 25.

Babacar Gueye, a constitutional expert and coordinator of a civil society collective which opposed the vote delay, described the Council's decision as "historic".

"The Council did not set a deadline, it simply said 'as soon as possible'. This means both quickly and under the right conditions," said Gueye, one of the organisers of the Aar Sunu Election (Let's protect our election) collective.

Senegal has faced growing calls from major international partners to organise the vote as soon as possible.

If it does not take place before the end of Sall's current mandate, the president of the National Assembly, who will act as interim president, has 90 days to organise the election, Gueye said.

Sall, who has been in power since 2012, said he called off the vote over disputes about the disqualification of potential candidates and concern about a return to unrest seen in 2021 and 2023.

Government spokesman Abdou Karim Fofana said the Council had seemed to leave room for manoeuvre.

"There are institutions... if the Constitutional Council and the National Assembly have different points of view, he (the president) must be able to have the high ground," he told French radio station RFI.

Faced with mounting public anger, Sall previously expressed a desire to find ways of obtaining "appeasement and reconciliation".

Fofana said the president's offer of dialogue still stands.

But Amadou Ba, the representative of detained opposition figure Bassirou Diomaye Faye, said that "Macky (Sall) must organise the presidential election before the end of his mandate," the Walf daily reported.

Several detained government opponents were released from prison late on Thursday, AFP journalists saw.

Souleymane Djim, a member of the collective of families of political prisoners, put the number of released at 64.

The government denies there are political prisoners in Senegal.