Tens of thousands of demonstrators have rallied in Bolivia's main city, La Paz, in one of the biggest protests in weeks of unrest.
The protesters are vowing to keep up the pressure
Riot police used tear gas in clashes near the presidential palace, while a strike brought traffic to a standstill.
The mainly left-wing and indigenous protesters are demanding the nationalisation of the gas industry.
President Carlos Mesa has been discussing the possibility of an early election to quell the unrest.
The BBC's Elliott Gotkine, in La Paz, says the demonstration has been mostly peaceful but the atmosphere in Bolivia is becoming increasingly fraught.
He says the protesters threw stones at a street vendor for opening his kiosk and heckled a businessman for wearing a tie.
Protesters held banners saying "Nationalise Now" and "The People Demand Nationalisation".
Two weeks of road blocks have begun affecting the supply of fuel and food into the city, but the protesters have vowed to carry on.
President Mesa, in power for 19 months, sought to end the crisis on Friday by signing a decree to convene a special assembly to change the constitution.
However, protesters say they will continue their action until the constituent assembly is guaranteed by Congress and the country's natural gas resources are nationalised.
The demonstrators want reforms to give more power to the indigenous majority, who are mainly from the impoverished highlands.
They are also opposed to demands for greater autonomy by energy-rich Bolivian provinces in the east.
President Mesa met Church leaders and politicians on Sunday to discuss the possibility of a snap election.
Senate President Hormando Vaca Diez, who was at the meeting, said it was "an idea that is gaining momentum as a way out of the problem".
The main left-wing leader Evo Morales has backed demands for an early election.
"It is the only way we will find a political solution," he told reporters.
Roman Catholic Cardinal Julio Terrazas has called for an end to the protests, describing them as "pressure tactics that for weeks have choked the residents of La Paz and have hurt most of all the poor".