Hundreds of thousands of people have taken to the streets in Mexico to support the left-wing candidate in the disputed 2 July presidential elections.
"Hold on, the people are rising," they chanted as they marched to Zocalo, Mexico City's main public square.
Andres Manuel Lopez Obrador is seeking a full recount of the vote which saw him lose to conservative Felipe Calderon by half a percentage point.
The Federal Electoral Institute has until 31 August to decide.
The dispute has paralysed Mexican politics, correspondents say.
A president-elect must be declared by 6 September to replace Vicente Fox on 1 December.
This was the third - and the largest - protest by Mr Lopez Obrador's supporters to press their demand for a recount.
Holding banners that read "No to fraud", and wearing T-shirts with the image of their candidate, they made clear they would not give in until a vote-by-vote recount was authorised.
"The elections were filthy," said Maria Teresa Priego. "We are here to support a humble man, a hard-working man."
Other voters were more belligerent.
"We will take drastic measures. We will blockade airports, we will take over embassies," threatened Sara Zepeda, 32.
The official count gave Mr Calderon 244,000-vote victory over his opponent - out of 41 million ballots cast.
The leftist candidate says there is evidence that vote counts were rigged at about half of the country's polling stations - but European Union observers have said they found no irregularities.
Mr Calderon has rejected calls for a recount, describing the election as "clean, free and democratic".