An assembly drafting a new constitution in Bolivia has been meeting for the first time in months, after moving to a military school amid security concerns.
Demonstrators in Sucre want to reclaim the title of capital city
A number of arrests were made and police fired tear gas in clashes with students. Several people were injured.
The assembly's efforts have been blighted by protests, prompting the ruling party to move Friday's session to a military building outside Sucre.
Protesters are demanding that the city be made Bolivia's sole capital.
Opposition politicians are boycotting the assembly's heavily-guarded session.
It was one of the central demands of the mass social movements which helped to get President Evo Morales elected in 2005 that Bolivia's constitution be rewritten to give more rights to the indigenous majority.
A constituent assembly was elected and established some 16 months ago to draft a new charter.
It had been due to deliver a draft new constitution at the beginning of August this year.
But repeated demonstrations over the proposed changes have disrupted the work of the assembly, which is now due to deliver its draft in December.
There is disagreement about which city should be Bolivia's capital
One of the key sticking points has been the designation of the country's capital.
Sucre has seen weeks of unrest, with protesters taking to the streets in support of an opposition proposal to make the city the sole capital of Bolivia.
Sucre, currently home to the Supreme Court, was Bolivia's capital until 1899 but since then has shared the title with La Paz.
Demand for the return of the seat of government to Sucre has fuelled a regional rivalry between President Morales' supporters in Bolivia's poor western highlands and his opponents in the more prosperous east.
There have also been counter-demonstrations in La Paz, where protesters say switching the capital from Bolivia's largest city, with a population of 1.7 million, to Sucre, population 250,000, would be expensive and divisive.