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Vice President Carlos Mesa (search) took office as Bolivia's new president late Friday but quickly proposed holding early elections, hours after his predecessor was forced out by weeks of bloody street protests set off by a plan to export natural gas to the United States.

Gonzalo Sanchez (search) de Lozada stepped down when he lost the support of his last key ally and his beleaguered government collapsed, sparking widespread celebrations in the streets.

Congress, in emergency session, accepted the 73-year-old leader's resignation and quickly named Mesa to the top post. As vice president, Mesa was next in the line of succession.

Wearing the red, yellow and green presidential sash, Mesa addressed lawmakers, calling for unity for solve the country's worst crisis since Bolivia returned to democracy in 1981.

"I'm taking office at a crucial time in Bolivia's history. ... My first obligation is to listen to what the thousands of people have said during the last few weeks," he said, referring to the demonstrators who have marched throughout the country since late September. More than 65 people were killed in rioting.

Mesa, a former television reporter and a respected historian, is a political independent and it wasn't immediately clear how much political support he will have. It also wasn't known how long he will serve. The elected term was until June 2007, but the bearded and bespectacled leader said he favored an earlier vote that he said would be "clean and transparent." Mesa did not give more details or say when the vote might be held.

"Our destiny is at stake. I urge you all to help me," he told lawmakers.

As word of the resignation spread, thousands swarmed La Paz (search) streets and avenues. Explosions boomed over the old Spanish colonial buildings as miners in hard hats lit sticks of dynamite, amid cheering by students, peasants, laborers and other opponents of Sanchez de Lozada.

"He's gone! He's gone," Indian women in bowler hats chanted alongside men and children.

Sanchez de Lozada complained in his two-page letter that letter to Congress that his resignation was forced and unfair.

"I do this unwillingly," he said, warning that Bolivian democracy was undergoing a "crucial hour," tested by the intense pressure by laborers, unions and other groups.

Several spectators in the gallery and lawmakers shouted "Goni! Assassin" using the president's nickname during the session, in reference to as many as 65 deaths reported by human rights groups from days of rioting.

The president's resignation came after thousands of Bolivians marched through La Paz for a fifth straight day Friday, demanding Sanchez de Lozada step down 14 months into his second term. Columns of students, Indians and miners brandishing sticks of dynamite threaded past street barricades, shouting, "We will not stop until he's gone!"

On a day when pandemonium ruled the La Paz streets, military planes airlifted hundreds of stranded foreigners from Bolivia's capital.

The U.S. military dispatched an assessment team to Bolivia on Friday to determine if plans need to be updated for protecting or evacuating the American embassy, a military spokesman said.

The team of fewer than six military experts will assess the situation on Bolivia's streets and recommend possible changes to the embassy's evacuation and protection plans, said Army Lt. Col. Bill Costello, a spokesman for U.S. Southern Command.

On Thursday, the U.S. State Department warned Americans to defer travel to Bolivia.

The popular outrage against the president was sparked by a controversial proposal to export gas to the United States and Mexico through neighboring Chile.

The proposal tapped deep discord with Bolivia's decade-old free-market experiment, which has failed to narrow the enormous gap between rich and poor in this impoverished country.

The proposal also underscored spreading popular distrust with his administration's U.S.-backed anti-coca growing policies, which have deprived thousands of poor Indian farmers of their livelihood and plunged the president's popularity ratings into the single-digits.

Sanchez de Lozada temporarily suspended the gas export plan last week in the face of riots, which human rights groups said claimed more than 65 lives. But the demonstrations for his resignation continued as many people objected to the government's heavy-handed response to the protests.

Late Wednesday, the president sought to defuse the growing crisis with a nationally televised address in which he offered to hold a national referendum vote over the plan. But opponents rejected that offer.

In defending the gas export plan, the president called the gas resources "a gift from God" that would bring millions of dollars annually to a cash-strapped Andean country. But few here believe his claims that average Bolivians, many of whom earn only a few dollars a day, would benefit.

Bolivia, which declared its independence from Spain in 1825, is a majority indigenous country where many speak Spanish haltingly. The country yielded its vast mineral wealth to its colonial rulers -- and many see the gas-export project as a return to that legacy.

Opponents also object to the use of Chile, a longtime rival, to export the fuel and argued the $5 billion project would only benefit wealthy elites.

The president suffered a final blow Friday when Manfred Reyes Villa, a key presidential supporter in Congress, said he was quitting the government.

"I've come to tell him: 'No more,"' Reyes Villa said. "The people don't believe in this government anymore and there is no other option but for him to resign."

On Thursday, presidential spokesman Mauricio Antezana also resigned.

Reyes Villa's departure left the president isolated as he sought to defuse the crisis in this Andean nation of 8.8 million people -- South America's poorest.

A U.S.-educated millionaire, Sanchez de Lozada was president from 1993 to 1997. He took office for a second term in August 2002 after narrowly defeating Evo Morales, a radical congressman.

Early Friday, a Brazilian air force plane flew 105 people out of Bolivia. Brazilian officials said 53 of those people were Brazilian tourists trapped in La Paz after all commercial flights in and out of the nearby El Alto international airport were halted last weekend.