Rwandan police have arrested twelve supporters of the main opposition challenger in the presidential election, Faustin Twagiramungu, ahead of Monday's vote.
Preparations for Monday's vote are in their final stages
"They were planning to coordinate acts of
violence in all the provinces tomorrow, " said a police spokesman quoted by the French news agency AFP.
But Mr Twagiramungu - an ethnic Hutu former prime minister - said the 12 were his provincial election observers and their arrests meant the poll could not be free and fair.
Final rallies took place on Saturday after a campaign marred by allegations of intimidation for the country's first presidential vote since the genocide of 1994, which left an estimated 800,000 Tutsis and moderate Hutus dead.
"This is a giant step that Rwanda has taken in
building democracy," Mr Kagame - a former Tutsi rebel leader - told crowds on Saturday.
However Amnesty International has accused Mr Kagame's ruling Rwandan Patriotic Front of using tactics including death threats to undermine the opposition.
Mr Twagiramungu, who returned from exile this year, has been accused by the Rwandan authorities of fomenting ethnic divisions - a charge he denies.
The BBC's Ishbel Matheson in the Rwandan capital Kigali says no-one seriously doubts that Mr Kagame will win.
However the international community will be watching closely to see whether the poll marks the beginning of a genuinely democratic society or whether it is simply the consolidation of President Kagame's grip on power, our correspondent says.
The campaign workers for Mr Twagiramungu who were arrested on Saturday have not yet been charged with any crime.
The arrests followed accusations levelled against Mr Twagiramungu by head of the electoral commission Chrysologue Karangwa that he was planning to sabotage the vote - a claim the candidate denied.
Election observers from the European Union have acknowledged that the run-up to the poll has not been without problems.
"You cannot speak of democratic elections in the classic sense of the word. That requires opposition, and there is no opposition," said Nellie Maes, a Belgian member of the European Parliament in Rwanda to observe the poll.
Paul Kagame has effectively exercised power in Rwanda since 1994 when he took control of the capital at the head of a rebel movement - the Rwandan Patriotic Front (RPF) - ending the genocide.
He then served as defence minister and vice-president, with the presidency going to a moderate Hutu Pasteur Bizimungu, who had held a series of senior RPF posts.
However Mr Kagame was appointed president in 2000 after Mr Bizimungu resigned.
Mr Kagame's well-financed campaign has included e-mail debates, text messaging and huge advertisements on the streets, plus air time on state-run radio and television.
Analysts say his ruling RPF has a tight grip on the press and that many Rwandans fear they will be accused of being "divisionist" if they do not support Mr Kagame.
On Sunday Alivera Mukabaramba withdrew from the race and advised her supporters to back Mr Kagame, her spokesman said.
Her withdrawal leaves only one other candidate in the race apart from Mr Twagiramungu - Jean Nepomuscene Nayinzira.