The protesters - mainly poor indigenous groups, farmers and trade unionists - are accusing the opposition of trying to stall plans for agrarian reform.

Evo Morales, the country's first indigenous president, was elected earlier this year on a platform pledging to redistribute land.

However these plans have been fiercely opposed by landowners.

Protesters from Bolivia's poor, indigenous majority, accuse the opposition and land-owning classes of trying to block Mr Morales' plans.

Santa Cruz is a stronghold of the opposition.

But correspondents say the roadblocks also put pressure on the government to deliver on its promises.

At present Mr Morales is restricted to handing out state-owned land, and so far Congress has failed to back plans to redistribute privately-owned land deemed to be unproductive, obtained illegally or used for speculation.

Mr Morales has vowed to redistribute 200,000 sq km - an area double the size of Portugal - by the end of his term in 2011.

But the programme has enraged landowners, with Bolivia's main landowners' federation pledging to form "self-defence groups" to defend their land.