Mexicans mount huge protest over threat to left-wing mayor

Mexico is heading for political crisis after its Congress voted to impeach the leading candidate in next year's presidential election in what his supporters said was a naked act of obstruction.

Mexico is heading for political crisis after its Congress voted to impeach the leading candidate in next year's presidential election in what his supporters said was a naked act of obstruction.

Congress voted 360-127 to strip Andres Manuel Lopez Obrador of legal immunity, opening the way for his arrest on a technicality and imprisonment. Such a development would probably deny him the right to run in the election as, under Mexican law, people facing charges are prevented from running for office.

Mr Lopez Obrador, the populist Mayor of Mexico City, told several hundred thousand supporters in the capital's central square that if a judge ordered his arrest he would turn himself in and act as his own lawyer. He called on them to launch a peaceful campaign of civil resistance including a "silent march" on 24 April.

"[Do not] fall into this trap and take radical measures that will scare people away and cause us to lose our popular support, so they can depict us as violent and quarrelsome," he said.

Thursday's decision by Congress is hugely important. What is at stake is whether Mexico will join other Latin American counties, such as Venezuela, Brazil and most recently Uruguay, in electing a leftist president, something opposed by members of the country's business community. Some observers believe the crisis will be the sternest test yet for Mexico's nascent democracy. When President Vicente Fox was elected in 2000 he ended 71 years of rule by the Institutional Revolutionary Party (PRI).

The Attorney General's office said it would immediately seek an order for Mr Lopez Obrador's arrest, relating to his breach of a 2001 court order prohibiting the building of a hospital access road on disputed land.

The move by Congress, and the potential for his arrest, could play to the advantage of Mr Lopez Obrador, a member of the Party of the Democratic Revolution. He has been quick to align himself with the politicians who struggled for democracy. "I am proud to be accused, like those who struggled for justice in the past," he told Congress before storming out. "Today you are judging me, but don't forget that history will judge both of us."

Larry Birns, the director of the Council on Hemispheric Affairs, a Washington think-tank, said: "The attempt to marginalise Lopez Obrador [has built] a local candidate into a national candidate. It is a mistake that the government is allowing this charge to be brought. Everybody knows the case against him is so minor and that this is simply electoral manoeuvring on the part of the ruling party."

The mayor's support has been built on public works projects and help for the poor. On Thursday, when he formally announced his presidential candidacy, he proposed "a homeland for the humiliated". He has said he will develop a more state-supported economy, greater reliance on oil revenues and a renegotiation of free trade pacts.

Some Lopez Obrador supporters believe the Bush administration had an influence in drumming up the effort to undermine him. However, the US Secretary of State, Condoleezza Rice, has said Washington could work with a left-wing president.Polls put Mr Lopez Obrador ahead of leading candidates from Mexico's two other major parties, the PRI and Mr Fox's conservative National Action Party. Mr Fox is prevented by law from running again.