Agbéyomé Kodjo made the accusation against President Faure Gnassingbé who has been in power since 2005 when he took over from his father.
The president’s office is quoted by AFP news agency as denying the accusation.
Provisional results indicate that Mr. Gnassingbé has won a fourth term.
Early on Monday, the electoral commission said that Mr. Gnassingbé had received 72% of the vote, compared with about 18% for Mr. Kodjo.
Mr. Kodjo, former prime minister and head of the national assembly, also accused the authorities of ballot stuffing and getting people to cast multiple votes in Mr. Gnassingbé’s favor.
Troops surrounded Mr. Kodjo’s home for around three hours after voting finished on Saturday.
Togo’s Security Minister, Yark Dameham, told Voice of America that Mr. Kodjo’s house had been surrounded as a precaution.
“We have received reports that he is at risk of an attack on his house by unruly individuals, but I cannot tell you from which side,” he is quoted as saying.
But Mr. Kodjo told the BBC that he was given no explanation and believed this was not for his protection but instead to allow time to rig the vote.
Mr. Gnassingbé has led Togo’s population of eight million people since taking over following the death of his father Gnassingbé Eyadema, who ruled for 38 years.
He faced six rivals for the position of president.
Constitutional changes were approved last year allowing him to seek re-election and potentially stay in office until 2030 – an issue which sparked huge protests in 2017-18.