Lomé, March. 07 (AFP) -- Security forces in Togo fired teargas on hundreds of protesters on Sunday as the opposition vowed to contest the results of an election won by the west African nation's President Faure Gnassingbe.

Jean-Pierre Fabre, the main defeated candidate in the poll who was at the protest, took shelter in the party headquarters of the Union of Forces for Change (UFC) along with other opposition leaders after armed riot police moved in.

There were between 200 and 300 opposition supporters at the protest.

The crackdown came as the UFC threatened a wave of protests against Gnassingbe, who first came to power amid violent clashes that left hundreds dead in 2005 and is the son of the country's former strongman leader.

Gnassingbe was returned to office in Thursday's election with 60.9 percent of votes cast, defeating his main rival Fabre who took 33.94 percent, according to official results announced on Saturday.

But Fabre accused the official electoral agency CENI of falsifying the results of the poll, seen as a test of democracy for Togo, which was ruled for four decades by Gnassingbe's father.

"I do not recognise the so-called victory of Faure Gnassingbe," he told hundreds of supporters at the headquarters of his party.

"I have never wanted to use violence, but if I am stolen from, I will not give up the fight," warned the opposition leader, an economist.

"We are going to stage protests, we are not going to take this lying down."

"I totally contest the figures," said Fabre, who claimed to have obtained between 55 and 60 percent of the vote.

Ayih Folly, a 23-year-old activist, said: "If they think it is all over, they are mistaken.... We shall mobilise ourselves and pour on the streets to show them this time round that our victory is dear to us."

A young opposition protester near UFC offices told AFP: "Even if we are only three, we shall fight till the end. It is either Faure (Gnassingbe) goes or death."

In the same area, a woman screamed: "I myself will protest, even with bare hands until we take power. Lome rejects the family of Gnassingbe, in power since 43 years."

In another part of town, a young Gnassingbe supporter -- in a black tee-shirt emblazoned with the president's picture -- warned his camp was ready to fight back.

"They accuse us each time that we stole their votes, threatening to pour on the streets," said Evariste Adoul. "We shall show them that we also can take to the streets."

As tensions mounted, UN Secretary-General Ban Ki-moon called for "calm and restraint" and for any grievances to be dealt with through legal channels.

Gnassingbe is the 43-year-old son of former leader Gnassingbe Eyadema, who ruled with an iron fist for 38 years over the poor country of 6.5 million.

Bloody unrest broke out in the capital of 1.5 million people following his election in 2005, claiming between 400 and 500 lives, according to the UN.

Thursday's election passed off without major violence but observers from regional bloc ECOWAS reported problems with ballot papers and a dozen opposition activists have been arrested since Saturday.

Riot police have been deployed across the seaside capital, where the streets were deserted for fear of violence. Another protest was teargassed on Saturday.

Security forces arrested the two main leaders of a UFC-linked youth movement, Dupuy and special forces commander Colonel Yark Damehane said.

They also picked up another 10 people including two aides to a defeated fringe candidate in the election, Messan Agbeyome Kodjo of the OBUTS movement.

Dahemane told AFP Kodjo's aides were detained for "distributing tracts and leaflets calling for a general uprising."

Kodjo, a former prime minister, accused the authorities of intimidation.

"These were not tracts, it was a statement signed in my name. This is arbitrary, it is an act of intimidation," he told AFP.

Dupuy also accused activists of the ruling Rally for the Togolese People of "intimidating and hunting UFC activists" in the Bassar region in northern Togo