The protesters carried banners and blocked a road, demanding a recount of all votes in the disputed 2 July poll.

The left-wing candidate rejected the tribunal's decision to recount only 9% of votes. "The Mexican people do not want only part of the truth," he said.

His supporters' sit-ins have paralysed the capital for the last week.

Official election results gave victory to the conservative Felipe Calderon by half a percentage point.

"Our institutions cannot remain subject to the power of money, to those who think they own Mexico," Mr Lopez Obrador told protesters gathered in the rain.

"If we permit it we will be accepting a simulated democracy, a democracy of lies."

'Longer' struggle

A spokesman for the coalition backing Mr Lopez Obrador said the civil disobedience would intensify.


The crowds shouted about "revolution"
"What is going to happen if they ratify this imposition?" Mr Lopez Obrador asked the crowd.

"Revolution!" his supporters shouted raising their fists aloft - although he has repeatedly urged them to remain peaceful.

On Sunday Mr Lopez Obrador asked his supporters to prepare "for a struggle that may last longer".

They have blockaded key streets in Mexico City for the last week, costing the city an estimated $23m (£18m) a day as traffic jams choke the city centre.

Fraud claims

Results from the July election showed that Mr Lopez Obrador lost to Felipe Calderon by less than 0.6 of a percentage point - or about 240,000 votes out of a total electorate of 41 million.

UN and EU observers pronounced the election free and fair.

However Mr Lopez Obrador presented some 900 pages of alleged evidence of electoral irregularities to the Federal Electoral Tribunal in the hope that it would order a full recount.

But on Saturday the tribunal ruled that only the results from 11,839 polling stations - of a total of 130,500 - should be recounted, beginning on Wednesday.

The tribunal has until 6 September to make its final ruling on the winner.

Analysts say if widespread irregularities are discovered, the judges could order a more sweeping recount.