Niger’s military is set to vote in a referendum on President Mamadou Tandja’s bid to serve a third term.
The government says the soldiers are voting early so they can ensure the safety of the rest of the people, who will go to the polls on Tuesday.
Earlier, opposition groups reiterated they would boycott the vote, which they have described a coup d’etat.
Mr Tandja has recently dissolved parliament and the constitutional court to push through his referendum plan.
He says the people of Niger want him to stay in power, and his actions reflect their will.
But his efforts have caused widespread protests in Niger and sparked international condemnation.
Reports from the country said huge posters of Mr Tandja were plastered throughout the capital, Niamey, and other main cities.
Mr Tandja’s backers say he has reduced poverty
State media has been calling on voters to say "yes" to changing the constitution so the 71-year-old president can stay in office.
The move would allow him an initial three-year term, and then he would be able to run for re-election with no term limits.
The AFP news agency reported that opposition leader Mahamadou Issoufou launched a final appeal on Sunday for "mobilisation to cause the illegal referendum to fail".
Speaking for the blanket group Co-ordination of Democratic Forces for the Republic (CFDR), he said: "Our duty as citizens is to defend the current constitution."
Mr Tandja was first elected in 1999, and then again five years later.
He had previously promised to quit in December this year, a month after presidential elections are due to be held.
But the president’s supporters argue he should be allowed a third term, saying he has improved living standards in one of the world’s poorest countries in the country in the 10 years he has been in power.