Sall's decision to push back the February 25 vote plunged Senegal into a crisis which has sparked deadly clashes between demonstrators and police.
"We are deeply concerned about the tense situation in Senegal," Liz Throssell, spokeswoman for the United Nations rights office, told reporters in Geneva.
"Following reports of unnecessary and disproportionate use of force against protesters and restrictions on civic space, we call on the authorities to ensure that they uphold Senegal's long-held tradition of democracy and respect for human rights," Throssell said.
She said at least three young men were killed and 266 people, including journalists, reportedly arrested across the country.
"Investigations into the killings must be prompt, thorough, and independently conducted, and those found responsible must be held to account," Throssell said.
"The authorities should also ensure due process for individuals arrested during the protests."
Throssell said the government must "unequivocally order the security forces to respect and ensure human rights, including the rights to freedom of expression, association and peaceful assembly."
She also voiced concern that mobile internet access in Senegal was on Tuesday suspended for the second time this month, after authorities banned a planned march against the election delay.
"It is really important to guarantee the right to access to information," Throssell said, insisting that any restrictions must be "strictly limited to what's necessary and (be) as limited as possible in time."
Senegal protest march over vote delay postponed
UN concern come as a protest march called on Tuesday against Senegalese President Macky Sall's move to delay this month's presidential poll to December has been postponed after authorities banned it, organisers said.
Elymane Haby Kane, one of the organisers of the march, told AFP he had received an official letter from local authorities in the capital Dakar that the march was banned as it could seriously hamper traffic.
"We will postpone the march because we want to remain within the law," said Malick Diop, coordinator of a collective that called the protest.
"The march was banned. There's a problem with the route. So we will change this," he told AFP.
The Aar Sunu Election (Let's protect our election) collective, which includes some 40 civil, religious and professional groups, had called for a rally in Dakar on Tuesday at 1500 GMT.
The United States and the European Union have called on the government to restore the original election timetable.
Sall said he postponed the election because of a dispute between parliament and the Constitutional Council over potential candidates barred from running, and over fears of a return to unrest seen in 2021 and 2023.
Parliament backed Sall's suspension of the election until December 15, but only after security forces stormed parliament and detained some opposition lawmakers.
The vote paved the way for Sall -- whose second term was due to expire in April -- to remain in office until his successor is installed, probably in 2025.
Senegal's opposition has decried the move as a "constitutional coup" and suspects it is part of a plan by the presidential camp to extend Sall's term in office, despite him reiterating that he would not stand again.
'End the violence'
Sall, who has been in power since 2012, is now seeking a way out of the turmoil.
Media have reported the possibility of a new dialogue with the opposition, including anti-establishment firebrand Ousmane Sonko, who fought the state for more than two years before being imprisoned last year.
Some have suggested the possibility of an amnesty for Sonko, his imprisoned second-in-command Bassirou Diomaye Faye and for people detained during unrest in 2021 and 2023.
The government has not commented on the reports.
Senegal's eight public universities began a two-day strike on Monday in protest over the death of a student during Friday's unrest in the northern city of Saint-Louis, the main higher education union said.
Academics posted a video on social media demanding "the immediate restoration of the electoral timetable" and respect for human rights.
Human Rights Watch meanwhile said at least 271 people were arrested on Friday and Saturday.
Ex-presidents Abdou Diouf and Abdoulaye Wade -- the father of one of the disqualified candidates, Karim Wade -- called on Sall to organise the "national dialogue he has announced, without delay", according to a letter sent to AFP and attributed to the former leaders.
They also called on youths to "immediately end the violence."
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