Campaigning has ended in Mauritania, a day before voters head to the polls to decide on controversial constitutional reforms.
The referendum, called for by President Mohamed Ould Abdel Aziz, seeks to abolish the senate and change the country's flag, among other changes.
Aziz contends that the changes are needed to make the government stronger, but opposition parties argue that if implemented, the changes will give the president sweeping powers and the government will slide towards dictatorship.
"When a leader violates the contract he has with the people and he wants to stay against the will of the people, this opens the door for more disturbance," Mohamed Jamil Mansour, president of the coalition forum, told Al Jazeera's Rob Matheson.
The opposition fears that if the senate is disbanded, the president will try to remain in control for a third five-year term, which he cannot do under the current constitution.
"While he thinks of another term in office, there's a risk of disturbance," Mansour said.
But Aziz has said that extending his rule is not why he called for the referendum.
"Lots of lies have been told to you," he said at a rally of pro-reform supporters.
"You have been told that the president is doing this to stay in power for third team. All of this is lies. It's lies."
Suppression of dissent
Aziz called for the referendum after the senate rejected the proposed changes in March, an apparent surprise to the president whose party maintains the majority.
Opposition parties have held several protests against the constitutional changes in advance of Saturday's vote.
On Thursday, the UN human rights office expressed concern over the ongoing unrest in Mauritania and the "apparent suppression of dissenting voices and the reported use of excessive force by the authorities against protest leaders".
Ravina Shamdasani, a spokeswoman for the Office of the UN Commissioners for Human Rights, said that "the authorities reportedly did not respond to the majority of requests for authorisation for the protests and actively dispersed gatherings".
She said that in "several cases, protest leaders were reportedly beaten up and a number of them were arrested".