The court's seven judges rejected demands to re-open every ballot box across Mexico and instead ordered a recount next week at 9 percent of the almost 130,500 polling stations.

Leftist challenger Andres Manuel Lopez Obrador wants a full recount of the more than 41 million votes cast in the July 2 election. His conservative ruling party rival Felipe Calderon won a razor-thin victory, but Lopez Obrador claims massive fraud.

The electoral court could still order many more ballot boxes opened.

Dozens of leftists shouted "Traitors!" outside the court building after the ruling.

"Without a solution, there'll be revolution," they yelled.

Lopez Obrador, a fiery anti-poverty campaigner and former mayor of Mexico City, has repeatedly said he would not accept a partial recount, raising fears of prolonged public unrest.

His supporters shut down central Mexico City all week and are threatening to extend the protests.

"Not just a small part of the vote returns, we want all the polls re-opened," Lopez Obrador told thousands of supporters on Friday night in the capital's vast Zocalo square.

He met with his closest advisors on Saturday afternoon to plan his next move. Some supporters warned of violence ahead.

"We are not going to allow this. We want all the polling stations, all 130,000. They are closing the path to democracy and the only thing left to us will be violence because we are not going to back down," said Pilar Saavedra, a university office worker.

Demonstrators left four fake coffins outside the court building with the message: "Democracy, R.I.P."

CHAOS

Lopez Obrador supporters have occupied the Zocalo and set up camp along the middle of the main boulevard running through Mexico City's business district since Sunday, causing traffic chaos across swathes of the capital.

Fearing further unrest, the federal government has raised security at Mexico City's international airport, power plants and oil refineries.

Calderon won the election by less than 0.6 percentage point, but he insists his victory was clean.

His pro-business National Action Party backed the electoral court's ruling on Saturday.

"We hope this ruling helps clear up doubts and concerns about the cleanliness and transparency of the election," said German Martinez, a senior Calderon aide.

The recounts at 11,839 polling stations, largely in northern states won resoundingly by Calderon, will begin next Wednesday and be completed on Sunday.

If they show the leftist with more votes than in the original result, it will increase pressure to open more ballot boxes. But if the results are unchanged, Lopez Obrador would come under intense pressure to halt his protest campaign.

International observers said the election was fair and most Mexicans agree, but about 35 percent believe the vote was rigged and about half favor a full recount, opinion polls show.

The bitter dispute has split Mexico and challenged its young democracy just six years after the election of President Vicente Fox broke 71 years of authoritarian and corrupt single-party rule.

The electoral court's judges have a reputation for expertise and independence among legal experts. They must rule on all legal challenges by the end of August and declare a president-elect by Sept. 6.