HUNDREDS OF PROTESTERS clashed with police outside Mexico’s congress today ahead of Enrique Pena Nieto’s presidential inauguration, tossing Molotov cocktails while officers responded with tear gas.

At least five police officers and a protester were injured in the melee sparked by around 500 protesters, many in masks, throwing objects and Molotov cocktails outside the congress, which was surrounded by metal barricades.

One officer was hit in the face by a stone, while two others were struck by a Molotov cocktail. They were taken away in ambulances.

Two more officers were carried out by their colleagues, apparently affected by the tear gas. A protesters appeared to have a head injury.

“We weren’t expecting something so violent,” an officer told AFP.

Pena Nieto’s presidency will mark the return of the Institutional Revolutionary Party, which ruled Mexico with an authoritarian hand for 71 years until it lost the 2000 presidential election.

The second-place finisher in this year’s election, leftist leader Andres Manuel Lopez Obrador, has refused to conceded defeat, charging that the PRI bought millions of votes. The electoral court threw out his claims.

The group that clashed with police was among thousands of protesters who took to the streets to protest Pena Nieto’s inauguration, chanting “Mexico without PRI!”

A protestor lies bleeding from his head after he was hit with a tear gas canister shot by riot police during protests (Image: Marco Ugarte/AP).

Inside the congress, some lawmakers held up protest signs against Pena Nieto, a telegenic 46-year-old lawyer and former Mexico state governor, before the ceremony.

Leftist lawmakers unfurled a giant black banner with crosses and the words “Imposition accomplished, Mexico in mourning.”

“A spurious government has concluded and the nightmare of imposition, illegitimacy and return to the past begins,” Deputy Ricardo Monreal, who was Lopez Obrador’s campaign manager, told the congress.

Lopez Obrador had lost the 2006 election to outgoing conservative president Felipe Calderon by less than one point and refused to accept that defeat too.

Six years ago, leftist lawmakers took over the legislature’s podium in a bid to disrupt Calderon’s swearing-in ceremony. This time, PRI lawmakers stood by the steps in an apparent effort to prevent a repeat.

Pena Nieto insists that the PRI – which governed with a mix of patronage, corruption and repression from 1929 to 2000 – has embraced democracy and will not return to its dark past.

“Today is a day of happiness, hope and innovation,” said Deputy Arturo Escobar of the Green Party, an ally of the PRI. “Mexico will change and grow.”

The new president inherits a brutal drug war that has left more than 60,000 people dead in the last six years.

Violence between the country’s powerful drug cartels surged after outgoing President Felipe Calderon launched a military offensive against the gangs when he took office in 2006.

Some lawmakers held up a banner that said: “Calderon, you leave a seat bathed in blood.”

- (c) AFP 2012.