The opening day of campaigning for Togo's presidential election has been marred by a confrontation between opposition supporters and security forces. The continuing violence renews doubts over the possibility of a free and fair vote later this month, following the death of the country's long-time ruler.

Hundreds of government security forces confronted marchers, who wore yellow T-shirts or scarves, the color of Togo's main opposition party. The opposition youths threw stones at riot police and army, who fired tear gas into the crowd.

Thousands of residents of Togo's capital, Lome, had heeded the call of opposition leaders to walk peacefully to city hall early Thursday to demand their voter cards and a delay to the presidential poll, scheduled for April 24.

But as has increasingly become the case in the more than two months since the death of longtime leader, President Gnassingbe Eyadema, violence broke out.

Thursday was the official opening day of campaigning for the first presidential election in four decades that will not feature Mr. Eyadema as a candidate. But of the four candidates eligible to run, only one, the late president's son, Faure Gnassingbe, was out on the campaign trail.

The remaining three, including the choice of the leading opposition Union of Forces for Change, Emmanuel Akitani-Bob, have boycotted the first day of campaigning, claiming Togolese authorities are rigging voter lists in favor of Mr. Gnassingbe.

Togo's minister of communications, Pitang Tchalla, says the opposition's allegations of voter fraud are nonsense. He says the government is doing everything possible to live up to the demands of ECOWAS. The West African regional bloc pushed for the poll as a condition for lifting sanctions it imposed after the military installed Mr. Gnassingbe to the presidency following the death of his father. He later agreed to step down in favor of the parliamentary speaker, who is designated under the constitution to become acting president until elections.

"We are not surprised. We agreed with ECOWAS," Mr. Tchalla said. "The government will respect its obligations to organize a very clear competition for everyone. And we refuse to fall into their game, into their way of confrontation."

But West Africa political expert Olly Owen agrees with the opposition it will be difficult to organize fair elections, given the current circumstances.

"That's not so much because of the violence and intimidation. That's an issue we'll see coming in later on, and it seems to be recurrent all the way through," he said. "But it's because of the electoral structures, which are basically tipped in such a way that it makes it impossible for the opposition to win."

Opposition candidate Mr. Akitani-Bob, who lost the 2003 presidential race to the late President Eyadema in polls widely criticized as rigged, says the people will not accept another fixed election.

He says the Togolese people are determined to see the end of what he calls a dictatorship that has lasted 40 years. And, he says, he cannot predict their reaction, if a winner is declared through fraud.