Jean-Pierre Fabre says he is confident of victory
Police in Togo have fired tear gas at supporters of the country's opposition presidential candidate Jean-Pierre Fabre, reports say.
Togo's opposition is alleging fraud as partial results from Thursday's presidential election come in.
With more than half of constituencies already declared, sitting President Faure Gnassingbe has a clear lead.
Both Mr Gnassingbe and Mr Fabre have claimed victory, with Mr Fabre alleging irregularities in the vote counting.
Counting has been delayed by a breakdown in the system transmitting figures from regions to the capital.
And results already declared show Mr Gnassingbe, the incumbent, with a clear lead even in Lome, seen as an opposition stronghold.
Mr Fabre said that a lack of adequate vote validation meant the count was now "illegal" and that "everything the electoral commission is doing is false".
Earlier, Jean-Claude Codjo, an opposition member of Togo's electoral agency, walked out of a meeting in protest at what he called a "lack of transparency".
The BBC's Caspar Leighton, in Lome, says that with riot police already firing tear gas and the final result yet to come, Togo is entering the most contentious phase of its election.
By Saturday afternoon, President Gnassingbe was leading with nearly 614,000 votes - about 52% - of nearly 1.19 million votes cast in 20 of 35 voting districts.
Mr Fabre had nearly 516,000 - or just over 43%.
Earlier, directors of voting districts were asked to bring ballot papers to the capital, Lome, after EU observers found a lack of transparency when results were submitted via satellite.
But Mr Codjo said he was concerned that officials came bearing their total tallies from all of the polling stations in each precinct, instead of ballots or counts from individual polling stations.
Faure Gnassingbe's family has been in power for more than 40 years
"I have no way of knowing if these numbers that are being read out are real. I say 'No.' I cannot accept this," he said.
EU observers had endorsed the VSAT satellite transmission system because it was believed to be tamper-proof.
But the system's machines malfunctioned and suspicions were raised of interference.
The opposition said they would not accept results sent by VSAT.
Mr Fabre, of the Union of Forces for Change (UFC), is seeking to deny a second term in office to President Gnassingbe, whose family has ruled the small west African state for more than four decades.
Mr Fabre's supporters feel they have been cheated of victory too many times in the past and should win this time, BBC West Africa correspondent Caspar Leighton says.
Mr Gnassingbe was put in power by the military upon the death of his father Eyadema early in 2005 after 38 years in office.
After widespread international condemnation, the son stood down and called elections which he won two months later. The opposition said the vote had been rigged.