LA PAZ, Bolivia -- Bolivia's government imposed martial law on a city of 750,000 outside the Andean capital Sunday after a series of deadly clashes between troops and demonstrators protesting plans to export gas to the United States and Mexico.

A total of 11 people, including a 7-year-old boy, have died since the protests began two weeks ago in El Alto, a poor industrial city 10 miles outside the capital, La Paz.

On Sunday, Bolivia put El Alto under military control as fresh clashes between troops and demonstrators broke out when soldiers dispersed hundreds of marchers.

Witnesses told local radio stations that one man was rushed to a hospital Sunday with a gunshot wound to his chest, but authorities did not confirm any new casualties.

The crisis also was causing a severe gas shortage and bringing public transportation to a standstill in the capital of South America's poorest nation, as demonstrators blocked roads to La Paz, preventing supplies from arriving.

The demonstrations are the latest to plague President Gonzalo Sanchez de Lozada, who grew up in the United States and has staked much of his political fortunes on his relationship with the Bush administration.

The leader has faced a series of violent protests by workers and indigenous leaders who say his free-market policies will not help the poor.

The government estimates the gas exports would earn about $1.5 billion for Bolivia.

But union and indigenous leaders reject the plan, saying the gas should be industrialized in Bolivia for the benefit of Bolivians.

They are particularly concerned that the government might decide to ship the gas out of a port in Chile. Bolivia has been a landlocked nation since it lost its coastline in a 1879 war against Chile, and resentment against its neighbor is still strong.

The government calls the protests unjustified, saying details of the project aren't even finished yet.

Presidential spokesman Mauricio Antezana accused demonstrators of trying to overthrow the government, an allegation the administration has made previously.

Antezana said the military decided to lock down El Alto after soldiers attempting to restore order earlier Saturday night were attacked with firearms and rocks by the demonstrators.

He said martial law was necessary "to ensure the safety of its citizens and protect public and private properties."

Riots Saturday between police and demonstrators left two dead, including the boy, and a protester who was shot in the head. Initial reports had erroneously said a police officer was killed.